Reactivity studies of η2-acyl complexes of molybdenum. kinetics of η2-acyl to η2-iminoacyl isomerization in their reactions with isocyanides

摘要

Reactivity studies of q2-acyl complexes of molybdenum. Kinetics of q2-acylto q2=iminoacyl isomerization in their reactions with isocyanidesMaria del Mar Conejo, Antonio Pizzano, Luis J. Sanchez * and Ernest0 Carmona *Departamen to Quimica Inorganica-Instituto de Investigaciones Quimicas, Universidad deSevilla- Consejo Superior de Investigaciones CientiJicas, Apdo. 553, 41071 Sevilla, SpainTreatment of the dihaptoacyls Mo{q2-C(0)R)L(C0)(PMe3), with carbon monoxide afforded the dicarbonylderivatives Mo{q2-C(0)R}L(C0),(PMe3) L = H,B(pz), or H,B(dmpz),; pz = pyrazolyl, dmpz = 33-dimethylpyrazolyl; R = Me, CH,SiMe3 or CH,CMe,. The analogous reactions with isocyanides, CNR',yielded two types of products, namely the acyl-isocyanides Mo{q2-C(O)R}L(CO)(CNR')(PMe,) or theq2-iminoacyls Mo{q2-C(NR')R)L(CO),(PMe3) (R' = CNC6H,Me-2,6, CNC6H40Me-p, CNCH,Ph orCNC,H, 1) depending upon the nature of the bis(pyrazoly1)borate ligand and the R group.Kinetic studies ofthe transformation Mo{q2-C(0)CH,SiMe,} { H,B(dmpz),}CO(CNR')(PMe,) --+ Mo{q2-C(NR')CH,-SiMe,} { H,B(drnpz),)(CO),(PMe,) (R' = 2,6-Me,C6H,) show first-order behaviour and are consistent witha mechanism involving deinsertion of CO to give a seven-co-ordinate alkyl intermediate in the rate-determiningstep.Transition-metal acyl complexes play an important role in anumber of organometallic reactions. Bidentate co-ordinationis usually the preferred binding mode of the acyl group incomplexes of the early transition metals,"2 including the 6dmetals. 3*4 Strong M-q2-C(0)R linkages are very oftenencountered and consequently many reactions of thesecompounds with Lewis bases proceed with substitution of otherligands without altering the co-ordination mode of the acylmoiety.Recent work from our laboratory has shown that theinteraction of the q 2-acyls Mo { q '-C(O)R} L(CO)(PMe,),L = unsubstituted and 3,5-dimethyl-substituted dihydro-bis(pyrazolyl)borate, H,B(pz), and H,B(dmpz), with CNBu'proceeds initially with PMe, displacement by the isocyanide,followed by isomerization to the thermodynamically morestable q'-iminoacyl-carbonyls Mo(~~-C(NBU')R}L(CO),-(PMe,). Since this report constitutes only the first well docu-mented example of an isomerization of this type, we havesought its generalization by the use of other isocyanides withdifferent electronic and steric properties and thereforemigrating capability.6 Here we discuss the results of this study,together with the outcome of the substitution reactions of theabove and other related q2-acyls of Mo with CO.Results and DiscussionThe new compounds described contain a bidentate bis(pyra-zoly1)borate ligand' and are of the types A-C.Scheme 1shows the synthetic procedure employed and includes alsothe combinations of the co-ligands which have been utilized.While acyls of composition M o { q '-C(O)R} L( CO)(PMe ,) ,(for every combination of L with R = Me, CH,SiMe3 orCH,CMe,) interact with CO to afford the correspondingdicarbonyl products A (Scheme l), the analogous reaction withisocyanides, CNR', may give compounds with structure Bor C.For example, in the H,B(pz), system all the reactionsinvestigated, which comprise those of Mo(q2-C(0)Me) { H,B-(pz),)(CO)(PMe,), with CNR' (R' = C6H,Me2-2,6 orC6H40Me-p) plus those of the neopentyl-derived q2-acyl withCNR' (R' = CH2Ph, C6H11 or C6H,Me,-2,6), provide theq2-iminoacyl (structure C) even when they are performed atlow temperatures (ca. - 10 "C). Hence, it seems clear that, forthese conversions, the initial substitution of PMe, by CNR'is followed by fast acyl-to-iminoacyl rearrangement to the1234567891011121314151617ARA 6' ,RL R COCNR'MeCH2CMe3MeCH2SiMe3CH2CMe3CH2SiMe3CH2CMe3CH2CMe3CH2CMe3MeMeCH2CMe3CH2CMe3CH2CMe3MeMeCH$3~!e3cococococoCNC6H,Me2-2,6CNCHghCNC6H3Me,-2,6CNC6H3Me,-2,6CNC,H,OMe-pCNCl-PhCNC6H3Me2-2.6C NC6H,Me,-2, 6CN C6H,0M e-pCNC6H,Me,-2,6CNC6H11CNC6H1,110; 11; 12; 13;14; 15; 18; 17Scheme 1 (i) CNR'; (ii) heatobserved q2-iminoacyl products.These results are in agreementwith those found in the interaction of the molybdenum q2-acylswith CNBu' although for the latter systems the bulkiness of theisocyanide fragment allows the isolation of stable q2-acyl-isocyanide compounds of type B.5J. Chem. SOC., Dalton Trans., 1996, Pages 3687-3691 368In turn, for the H,B(dmpz), system the interaction ofMo{q2-C(0)Me){H2B(dmpz)2)(CO)(PMe3)2 with CNR(R' = C6H,Me2-2,6 or C,H,OMe-p) also furnishes directlyq2-iminoacyls of structure C whilst treatment of Mo{q2-C(O)CH,SiMe,) { H,B(~~~z),)(CO)(PM~,)~ with CNC6H3-Me2-2,6 and of Mo{q2-C(O)CH,CMe,){H,B(dmpz),)-(CO)(PMe,), with CNR' (R = CH,Ph, C,H,, or C6H,Me,-2,6) allows the isolation of the expected q2-acyls with structureB.Hence, the facility with which the transformation of theacyls Mo{q2-C(O)R)(CNR') into the iminoacyls Mo{q2-C(NR')R)(CO) takesplace varies in the order H,B(pz), > H,B-(dmpz), and Me > CH,SiMe3 > CH2CMe3. Iminoacyl form-ation is therefore favoured for the least sterically demandingcombination of the L and R fragments. Finally, in this regard, itshould be mentioned that complex 6 converts slowly at roomtemperature into 17, while the q2-acyls derived from the bulkierneopentyl group, 7-9, are stable at room temperature withrespect to their transformation into the corresponding q2-iminoacyls.This rearrangement occurs however, at highertemperatures (ca. 60 "C) but it is still so slow that a competitivereaction leading to hydroboration of the q2-acyl fragment occurspreferentially. *All the transformations represented in Scheme 1 give highyields of the corresponding products which are usually isolatedby crystallization from Et20 or light-petroleum (b.p. 40-6O0C)-Et,O mixtures, in the form of red-orange or yellowcrystalline solids. They can be readily characterized byspectroscopy (see Experimental section). The IR spectra of theacyls Mo(q2-C(O)R}L(L')(CO)PMe, (L' = PMe,, startingmaterial; CO, structure A; CNR', B) display v(CO),,,, in theexpected region' of 1625-1450 cm-'.Within this range thestretching frequency shifts to lower wavenumbers as theelectron-donor properties of L' increase: L' = CO, 1600-1 560;CNR', 1580-1 550; PMe,, 1500-1480 cm-'. This clearly reflectsan increase in the same direction of the back donation from themetal centre to the acyl ligand. A parallel decrease is observed inthe value of v(C0) for the terminal carbonyl (ca. 1940 and 1850,L = CO; 1800, CNR'; 1775 cm-', PMe,). The q2-iminoacyls(structure C) are characterized by two strong terminal carbonylstretchings in the vicinity of 1925 and 1800 cm-' as well as bya medium-intensity absorption at ca. 1700 cm--' due to theiminoacyl ligand.This supports the dihapto binding modeproposed for this functionality. '3' Since compounds withstructures A and C have the same stereochemistry and differonly in the nature of the Mo-q2-C(X)R linkage, a comparisonof the donor properties of these two functionalities can beattempted. The already noted values of v(C0) (1940, 1850 forthe q2-acyls; 1925, 1800 cm-', q2-iminoacyls) indicate anoverall higher donor ability of the q2-iminoacyl entities ascompared to the analogous q2-acyl groups.Best support for the structures assigned to the abovecomplexes comes from NMR studies. Thus the q2-acyls displaythe 13C-{1H) resonance of the acyl carbon in the region 6 275-250, while for the q2-iminoacyls the Mo-',C(NR')R signalappears at 6 210-190. The above values are well in the rangecharacteristic of compounds of this type.For the dicarbonylcomplexes (A and C) the two carbonyls and the two pyrazolylrings of the L ligand are equivalent at room temperature. As forother q2-acyl complexes, this is probably due to a relatively low-energy fluxional process which creates an effective plane ofsymmetry. ' OAs already mentioned, of the isolated compounds withstructure type B the H,B(dmpz),-CH,SiMe, derivative 6 isthermally stable at room temperature for moderate intervals oftime, although it is converted into the q2-iminoacyl isomer 17over a period of several hours (t+ = 0.75 h). In order to gainmechanistic information on this isomerization reaction, inparticular with respect to the influence of the isocyanide ligandon the reaction rate, kinetic studies have been undertaken.Twoclosely related q 2-acyl-isocyanide derivatives were chosen:0.5-0.5- 0" 5 -1.5 v c --2.5 IL , ,,A f-3.5 i l L . l I I I I I I , l I I 1 , l . /0 400 800 1200t h i nFig. 1 First-order kinetic plots for the transformation of complex6 (B) and Mo{ q 2-C(0)CH2SiMe, 1 { H,B(dmpz), )(CO)(CNBu')-(PMe,) (A) into the corresponding iminoacyl complexescomplex 6 and the already reported Mo{q2-C(O)CH,SiMe,}-(H2B(pz)2)(CO)(CNBu')(PMe3).5 As can be seen, theycontain identical sets of co-ligands with the only exception ofthe isocyanide groups, CNR' (R = C6H,Me,-2,6 or Bu'), theirchoice being influenced by their very different insertionaptitudes. The greater propensity of the aromatic isocyanide,CNC6H,Me,-2,6, to undergo insertion reactions, as comparedwith the aliphatic CNBu', is well documented.6,"The rates of the two reactions can be conveniently measuredat room temperature by 31P-(1H) NMR spectroscopy.Bothtransformations follow first-order kinetics, the analysis of thedata (Fig. 1) recorded over a period of ca. four half-livesyielding rate constants of 1.84 x lo-, and 1.60 x s-' forthe CNBu' and CNC,H,Me,-2,6 derivatives. As expected,CNC,H,Me,-2,6 inserts faster than CNBu', but the differenceof only one order of magnitude in the kobs values seems inagreement with a rate-determining step involving deinsertion ofCO from the original q2-acyl to generate a sterically congestedseven-co-ordinate alkyl intermediate, followed by fast iso-cyanide insertion.This mechanistic hypothesis also findssupport in the already cited influence of the steric effects ofthe L and R fragments on the reaction rate.Experiment a1Microanalyses were carried out by Pascher MicroanalyticalLaboratories, Remagen, Germany, and the Analytical Serviceof the University of Seville. Infrared spectra were recorded asNujol mulls or in an appropriate solvent on a Perkin-Elmermodel 684 spectrometer. The 'H, I3C and ,'P NMR spectrawere run on a Varian XL-200 or on Bruker AMX-300 or AMX-500 instruments. The 31P shifts were referenced to external85 H,PO,, 'H and I3C shifts to the residual signals of thedeuteriated solvents employed, and are all reported in ppmdownfield from SiMe,.All preparations and manipulations were carried out underoxygen-free nitrogen or argon, following conventionalSchlenk techniques.Solvents were dried and degassed beforeuse.All reagents were either obtained from commercial suppliersor prepared according to published procedures. The com-plex Mo{q2-C(0)CH2SiMe,){H2B(dmpz)2)(CO)(CNBu')-(PMe,) used for the kinetic studies was prepared asreported previously. Analytical and spectroscopic data for thenew complexes are given in Tables 1 and 2.PreparationsMo{q2-C(0)R}L(CO),(PMe3), (structure A). Through asolution of Mo{q2-C(0)Me) {H2B(pz)2)(CO)(PMe,)2 (0.46g, 0.5 mmol) in tetrahydrofuran (thf) (50 cm3), carbonmonoxide was slowly bubbled at room temperature until the3688 J. Chem.SOC., Dalton Trans., 1996, Pages 3687-369Table 1 Analytical, IR and 'H NMR data for the compounds Mo(q2-C(O)R)L(CO),(PMe,), Mo{q2-C(0)R)L(CO)(CNR')(PMe3) andMo{q2-C(NR')R}L(CO),(PMe,)Analysis() aCompound C H N123456 d789101112131415 =161738.1(37.3)43.3(43.0)43.0(43.0)43.4(43.9)47.3(47.5)51.9(51.8)54.3(54.3)53.1(53.0)55.0(55.0)48.0(48.4)45.7(45.9)51.8(51.2)49.8(49.8)52.3(52.0)52.1(52.0)49.9(49.7)51.1(5 1.8)5.0 13.6(4.8) (13.4)6.0 11.8(5.9) (11.8)6.3 11.9(5.9) (11.8)6.9 10.6(6.6) (10.3)7.1 9.9(6.8) (10.6)6.7 10.6(6.9) (10.8)7.0 11.0(7.0) (11.3)7.8 11.7(7.8) (11.5)7.1 10.7(7.2) (11.0)5.5 12.9(5.6) (13.4)5.3 13.7(5.2) (13.4)6.2 11.5(6.3) (12.4)7.2 12.6(7.1) (12.6)6.6 12.1(6.5) (12.1)6.6 12.3(6.4) (12.1)5.6 12.2(6.0) (12.1)6.9 11.0(6.9) (10.8)IR data (Nujol)/cm-'vco~ ( c N R , )1940s1865s1934s1848s1934s1837s1934s1835s1940s1848s1810s2038s1820s2054s1804s208 1 s1822s2040s1932s1800s1937s1816s1928s1802s1932s1810s1924s1806s1932s1800s1914s181 1sVCORVIC(NR')Rl1600m1584m1600m1562m1600w1560w1567m1569m1580m1696m1720m1716m1718m1684m1691m1700m'HNMR(6)PMe,b R'2.73 (s)1.04 (s, CMe,),3.41 (s, CH,)2.85 (s)0.17 (s, SiMe,),3.30 (s, CH,)1.09 (s, CMe,),3.62(s, CH,)0.28 (s), 2.96, 3.76(d, 12.7, CH,)1.20 (s, CMe,), 3.22,3.82 (d, 17.8, CH,)1.28 (s, CMe,), 3.39,3.94 (d, 17.7, CH,)1.20 (s, CMe,), 3.42,4.01 (d, 17.9, CH,)2.34 (s)2.65 (s)1.06 (s, CMe,),2.89 (s)1.15(s, CMe,),2.90 (s)1.05 (s, CMe,),3.13 (s)2.92 (s)2.93 (s)0.05 (SiMe,),3.10 (s)R'2.25 (s,2 Me),6.75 (m, Ph)16.2, JHp = 3.2), 7.0(m, Ph)1.17, 1.38 (m), 1.60,3.35 (m)2.26 (s), 6.76 (AB,)(JAB = 7.7)1.63 (s), 6.75 (AB,)(JAB = 7.7)3.10 (s), 6.17 (m),6.44 (m)4.35 (s), 6.84 (m),6.96 (m)0.47 (m), 0.86 (m),1.31 (m), 3.27 (m)1.82 (s), 6.77 (s)4.25,4.29 (JHH =1.54 (s), 6.91 (s)3.10 (s), 6.17 (m),6.42 (m)2.08 (s), 6.78 (m)~ ~~L'5.91 (t), 7.41, 7.50 (d, 2.1)5.92 (t), 7.45,7.47 (d, 2.1)2.22, 2.25, 5.60 (s)2.26,2.32, 5.63 (s)2.25,2.28, 5.62 (s)2.19,2.30,2.34,2.59, 5.70,5.73 (s)2.16, 2.31, 2.34,2.53, 5.67,5.71 (s)2.24, 3.31,2.35,2.58, 5.68,5.73 (s)2.17, 2.26, 2.27, 2.31, 5.64,5.67 (s)5.87 (t), 7.52, 7.55 (d, 2.1)5.91,7.45, 7.67 (d, 2.1)5.88 (t), 7.38,7.51 (d, 2.1)6.00 (t), 7.51,7.65 (d, 2.1)5.94 (t), 7.51, 7.80 (d, 2.1)2.09,2.24, 5.71 (s)2.01, 2.37, 5.65 (s)2.21, 2.51, 5.70 (s)Solvent C6D6 unless otherwise stated.Calculated values in parentheses. Jc,/Hz in parentheses. JHH/Hz in parentheses. NMR data in C6D,CD3.NMR data in (CD,),CO.solution changed from red to yellow (2 h). The solvent wasthen removed in uacuo and the residue extracted with lightpetroleum-Et,O (1 : 1). Centrifugation and cooling at - 15 "Cafforded Mo~q2-C(0)Me~~H~B(pz)~~(CO)~(PMe~) 1, asyellow crystals in 70 yield.Complexes 2-5 were similarlyobtained as yellow crystals by carbonylation of thecorresponding monocarbonyl derivatives. They required,however, longer reaction times or alternatively higher COpressures ( 3 4 atm, ca. 3 x lO-'-4 x Pa), although in thelatter case the reaction yields were somewhat lower.Mo{q2-C(O)R}L(CO)(CNR')(PMe,) (structure B). Thecomplex Mo{q2-C(0)CH,CMe3} {H,B(dmpz),)(CO)-(PMe,),' (0.58 g, 1 mmol) was dissolved in thf (60 cm3)at room temperature and neat CNCH,Ph (0.1 cm3, 1mmol) was added directly to the stirred solution. After 15 minthe reaction mixture changed from red to dark yellow. Thesolvent was removed in oarno to produce a brown solid, whichwas crystallized from light petroleum-Et,O (2 : 1) to affordorange crystals of 7 in 60 yield.Adding the appropriate CNR' ligand to Mo(q2-C(0)CH,C-Me,) (H,B(dmpz),)(CO)(PMe,), allowed the preparation ofcomplexes 8 and 9 by the same procedure as orange crystals.They were isolated by crystallization from light petroleum-Et,O (1 : 1 ) in 78 yield (8) and from Et,O in 63 yield (9).Thesynthesis of the CH,SiMe3 derivative, 6, was accomplishedby the above procedure using Mo{ q2-C(0)CH,SiMe,}{ H,B-(dmpz),}(CO)(PMe,), ' as the starting material, but in orderto avoid further reactivity temperatures below 5 "C were,however, required during the work-up process. It was isolatedas orange crystals in 85 yield.Mo{q2-C(NR')R}L(CO),(PMej) (structure C). The com-pound CNC6H3Me,-2,6 (0.13 g, 1 mmol) was dissolved in thf(40 cm3) at room temperature and Mo{q2-C(0)CH,CMe3}-{H2B(p~)2}(CO)(PMe3), added.The resulting mixture wasstirred for 1-2 h at 60°C, the solvent was removed underreduced pressure and the residue extracted with light petroleum.Centrifugation and cooling at -35 "C afforded 14 as orangecrystals in 41 yield.Using the appropriate molybdenum complex ' and CNR' thefollowing compounds were obtained by the above procedure:10 (50), 11 (70), 12 (54), 13 (57), 15 (78), 16 (51) and 17 (90yield). They were isolated as orange crystalline solids from lightpetroleum with the only exception of the less-soluble derivative12, which required light petroleum-Et,O (3 : 1).Kinetic studies of the isomerization of the dihaptoacyl Mo{q2-C(0)CHfiiMe3}{H2B(dmpz)2~(CNR')(CO)(PMe~ (R' = Butor C6H3Me2-2,6) into the corresponding iminoacyl Mo{q2-In both cases, the disappearance of the acyl isomer wasmonitored at 24 "C by "P-{'H) NMR spectroscopy for aC(NR)CH2siMe,}CH2BO,)(CO),(PMe3) 1J.Chem. SOC., Dalton Trans., 1996, Pages 3687-3691 368Table 2 The "P-{ 'H) and 13C-( 'H} NMR data for compounds 1-17"C-{ 'H) (6),lP-{ 'H}Compound (6)12345678'9101112131415'161712.1 (s)10.2 (s)15.3 (s)12.1 (s)13.0 (s)1 1.2 (s)7.5 (s)13.7 (s)12.2 (s)3.2 (s)4.0 (s)2.2 (s)4.5 (s)0.9 (s)12.4 (s)7.6 (s)1.4 (s)R31.2 (s)29.5 (s, CMe,), 32.8 (s,CMe,), 60.2 (s, CH,)32.4 (s)-0.9 (s, SiMe,), 40.029.1 (s, CMe,), 3 1.6 (s,CMe,), 60.9 (s, CH,)-0.6 (s, SiMe,), 39.06, CH,)6, CH2)17.6 29.4(s, CMe,), 31.6 (s,(d, 28) m e , ) , 60.2 (s, CH,)17.5 29.5(s, CMe,), 31.6(s,(d, 28) CMe,), 60.1 (s, CH,)17.9(d, 29)29.6 (s, CMe,), 32.0 (s,CMe,), 61.0 (s, CH,)16.1 21.3(s)( 4 25)16.7 21.3 (s)(d, 27)17.2 30.1 (s, CMe,), 32.8 (s,(d, 26) me3),44.2(s,CH,)15.5(d, 24) CMe3),47.4(s, CH,)29.9 (s, CMe,), 33.9 (s,17.5 23.8 (s)(d, 28)17.7 23.2(s)(d, 28)16.0 -0.7 (s, SiMe,), 28.7(d, 23) 6, CH,)N-N R'" CX/C(X)R '105.0, 136.4, 143.3 (s)105.2, 136.5, 143.4 (s)12.6, 14.0(s, Me), 106.8, (s,CH), 144.9, 150.5 (s, CMe)14.4, 12.7 (s, Me), 106.3(s, CH), 149.8, 143.5 (s, CMe)12.6, 14.1 (s, Me), 106.3(s, CH), 143.4,149.7 (s, CMe)Me), 106.3, 105.9(s, CH),143.0, 143.4, 150.4, 150.86, m e )12.6, 12.8, 14.2, 14.8 (s, 192.2 (d, 26, CNR')Me), 105.9, 106.2 (s, CH), 233.3 (d, 20, CO)142.9, 143.2, 148.7, 150.7 268.3 (d, 13, COR)12.6, 12.8, 14.3, 14.7 (s, 183.6 (d, 27, CNR')Me), 105.8, 106.3 (s, CH), 233.3 (d, 21, CO)142.8, 143.1, 148.5, 150.8 2CH, ofC,H,,), 54.6(s,CH 269.5(d, 13, COR)13.0, 13.1, 14.6, 14.8 (s, 199.8 (d, 27, CNR')Me), 106.2, 106.5 (s, CH), 232.7 (d, 21, CO)143.2, 143.5, 149.1, 150.8 266.7 (d, 12, COR)6, m e )104.7, 136.4, 143.9 (s, CH)230.4 (d, 17, CO)254.0 (d, 13, COR)23 1.2 (d, 18, CO)255.8 (d, 12, COR)230.4 (d, 22, CO)262.0 (d, 11, COR)231.6 (d, 21, CO)258.1 (d, 10, COR)230.4 (d, 22, CO)260.8 (d, 10, COR)12.8, 12.9, 14.8, 14.9(~, 18.6(~, C,He,), 126.0,129.3 (s, 3CH ofC,H3Me,),132.6 (s, 2CCH, of C6H,Me,)48.5 (s, CH,Ph), 127.0 (s,2CH of Ph), 128.0 (s, CH ofPh), 128.7 (s, 2CH of Ph),23.5(s,2CH2 ofC6Hll), 24.7(CH, of C6Hll), 33.7 (s,(s, m e ) 134.6 (s, Cipso)6, m e ) Of C6HI 1)18.2 (s, 2CH3 Of C,H,Me,),126.1 (s, CH Of C,Me,),128.4 (s, 2CH Of C6H3Me,),130.6 (s, Cipso), 132.7 (s,CCH, of C,H,Me,)17.6 (s, 2CH3 Of Ce,),125.2 (S, CH Of C,H,Me,),128.0 (S, 2CH Of C6H3Me2),130.2 (s, CCH, of C,H,Me,)123.2(~,2CHofPh), 132.2(s, 236.1 (d, 19, CO)Cipso), 157.5 (s, COMe)52.3 (d, 3, CH,Ph), 126.8 (s, 201.3 d, 12, C(NR')R2CH of Ph), 128.2 238.3 (d, 18, CO)(s, 3CH of Ph), 135.8 (s, Cipso)206.7 (d, 11, COR)234.8 (d, 17, c o )104.7, 136.1, 143.7(s,CH) 54.4(s, CH,OPh), 114.3, 202.2 d, 12, C(NR')R104.3, 136.1, 143.7 (s, CH)104.3, 136.0, 144.1 (s, CH) 24.7(s,2CH20fC6H11),25.1 193.7 d, 11, C(NR')R2CH, of C6H1 '), 57.6 (s,18.2 (s, 2CH, O f C,H,Me,),125.3 (s, CH of C,H,Me,),128.0 (s, 2CH Of C,H,Me2),129.9 (s, CCH, of C,H,Me,)17.9 (s, 2CH3 Of C ~ H ~ M ~ Z ) ,125.9 (s, CH Of C6H,Me2),129.1 (s, 2CH of C6H3Me2),13 1.2 (s, 2CCH, Of C6H,Me,)54.3 (s, CH,O), 114.6, 122.6(s, 2CH of Ph), 131.8 (s,18.4 (s, X H , of C,H,Me,),124.9 (s, CH of C,H,Me,),128.5 (s, 2CH Of C ~ H J M ~ ~ ) ,130.1 (s, 2CCH, of C6H3Me2)(s, CH2 Of C,H11), 31.4 (s, 238.6 (d, 19, CO)3CH Of C6H11)104.6, 136.7, 144.2 (s, CH) 206.5 d, 11, C(NR')R238.0 (d, 17, CO)13.6, 15.7 (s, Me), 107.3 (s,CH), 145.2, 151.6 (s, m e )21 1.6 d, 12, C(NR')R236.5 (d, 20, CO)14.5, 13.0(s, Me), 105.8(s, CH), 143.9, 149.2 (s,m e ) Cipso), 157.0 (COMe)13.6, 16.6 (s, Me), 106.9(S, CH), 145.7, 151.7 (s,m e )205.5 d, 8, C(NR')R235.8 (d, 20, CO)204.8 d, 12, C(NR')R240.0 (d, 18, CO)Solvent C6D6 unless otherwise stated." Jcp in parentheses. ' In C,D,CD,. ' In (CD,),CO.period of about four half-lives. The two reactions were wellbehaved and produced the iminoacyl isomers as the onlydetectable products. Duplicate experiments were performed inboth cases. In a typical experiment, a solution of complex 6 inC,D, (around 0.08 mol dm-3) was transferred under N, into a5 mm NMR tube which was then frozen and degassed. In orderto avoid possible interference from an internal reference, acapillary containing a solution of PPh, in acetone (around 0.04mol dmP3) was introduced inside the NMR tube and employedas an external standard.The tube was sealed and placed into aNMR probe at 24 "C (uncertainty k 0.1 "C) and its 31P-(1H}NMR spectrum recorded on a Bruker AMX-500 spectrometer.In each experiment the acquisition was performed using aninterscan delay of about five times the slowest relaxation timeof the 31P nuclei.AcknowledgementsWe thank the Direccibn General de Investigacion Cientifica yTkcnica (Grant No. PB94-1436) and EU (Human MobilityProgramme Proposal No. ERB4050PL920650). We alsoacknowledge Junta de Andalucia for the award of research36W J. Chem. SOC., Dalton Trans., 1996, Pages 3687-369fellowships.Thanks are also due to the University of Sevilla forfree access to its analytical and NMR facilities.References1 L. D. Durfee and I. P. Rothwell, Chem. Reu., 1988,88, 1059.2 G. Fachinetti and C. J. Floriani, J. Chem. SOC., Dalton Trans., 1977,1946; J. A. Marsella, K. G. Moloy and K. G. Caulton, J. Organomet.Chem., 1980, 201, 389; J. M. Manriquez, D. R. McAlister, R. D.Sanner and J. E. Bercaw, J. Am. Chem. SOC., 1976,98,6733; 1978,100,2716; P. T. Wolczanski and J. E. Bercaw, Ace. Chem. Res., 1980,13, 121; G. Erker, Acc. Chem. Res., 1984, 17, 103 and refs. therein;F. Calderazzo, Angew. Chem., Int. Ed. Engl., 1977,89,299.3 E . Carmona, G. Wilkinson, R. D. Rogers, W. E. Hunter, M. J.Zaworotko and J. L. Atwood, J. Chem. SOC., Dalton Trans., 1980,229; E.Carmona, L. J. Sanchez, J. M. Marin, M. L. Poveda, J. L.Atwood, R. D. Riester and R. D. Rogers, J. Am. Chem. SOC., 1984,106, 3214; E. Carmona and L. J. Sanchez, Polyhedron, 1988, 7,163; E. Carmona, L. Contreras, M. L. Poveda, L. J. Sanchez,J. L. Atwood and R. D. Rogers, Organometallics, 1991, 10, 61;E. Carmona, L. Contreras, M. L. Poveda and L. J. Sanchez, J. Am.Chem. SOC., 1991, 113,4322; L. Contreras, A. Monge, A. Pizzano,C. Ruiz, L. J. Sanchez and E. Carmona, Organometallics, 1992,11, 3971.4 C. A. Russik, T. L. Tonker and J. L. Templeton, J. Am. Chem. SOC.,1986, 108, 4652; A. S. Gamble, P. S. White and J. L. Templeton,Organometallics, 1991, 10, 693; F. R. Kriessl, W. J. Sieber, M.Wolfggruber and J. Riede, Angew. Chem., Int. Ed. Engl., 1994, 23,640; T. Desmond, F. J. Lalor, G. Ferguson, B. Ruhl and M. Parvez,J. Chem. SOC., Chem. Commun., 1983,55; H. G. Alt, J. Organomet.Chem., 1977,127,349.5 A. Pizzano, L. J. Sanchez, M. Altmann, A. Monge, C. Ruiz andE. Carmona, J. Am. Chem. SOC., 1995,117,1795.6 P. P. M. de Lange, H. W. Friihauf, M. J. A. Kraakman, M. wanWijnkoop, M. Kranenburg A. H. J. P. Groot and K. VreiZe,Organometallics, 1993, 12, 417; P. P. M. de Lange, M. wanWijnkoop, H. W. Friihauf and K. Vreize, Organometallics, 1993,12,428; P. P. M. de Lange, R. P. de Boer, M. wan Wijnkoop, J. M.Emsting, H. W. Friihauf and K. Vreize, Organometallics, 1993, 12,440.7 S. Trofimenko, Chem. Rev., 1993,93,943.8 A. Pizzano, L. J. Sanchez, E. GutiCrrez, A. Monge and E. Carmona,Organometallics, 1995,14, 14.9 E. Carmona, P. Palma, M. Paneque and M. L. PovedaOrganometallics, 1990,9, 583.10 M. D. Curtis, K.-B. Shiuand W. M. Butler, J. Am. Chem. SOC., 1986,108, 1550; C. A. Rusik, M. A. Collins, A. S. Gamble, T. L. Tonkerand J. L. Templeton, J. Am. Chem. SOC., 1989,111,2550.11 P. M. Treichel, K. P. Wagner and R. W. Hess, Znorg. Chem., 1973,12, 1471; J. Dupont and M. Heffer, J. Chem. SOC., Dalton Trans.,1990, 3193; E. Singleton and H. E. Ooasthuizen, Adu. Organomet.Chem., 1983,22,209.Received 25th March 1996; Paper 6/02075EJ. Chem. SOC., Dalton Trans., 1996, Pages 3687-3691 369