Coordination features of a hybrid scorpionate/phosphane ligand exemplified with iridium

摘要

Although the pentacoordinated complex [Ir{(allyl)B-(CH2PPh2)(pz)(2)}(cod)] (1; pz=pyrazolyl, cod=1,5-cyclooctadiene), isolated from the reaction of [{Ir(mu-Cl)(cod)}(2)] with [Li(tmen)][B(allyl)(CH2PPh2)(pz)(2)] (tmen=NNN',N'-tetramethylethane-1,2-diamine), shows behavior similar to that of the related hydridotris(pyrazolyl)borate complex, the carbonyl derivatives behave in a quite different way. On carbonylation of 1, the metal-metal-bonded complex [(Ir{(allyl)B(CH2PPh2)(PZ)(2)}CO)(2)(mu-CO)] (2) that results has a single ketonic carbonyl bridge. This bridging carbonyl is labile such that upon treatment of 2 with PMe3 the pentacoordinated Ir-1 complex [Ir(CO){(pz)B(eta(2)-CH2CH= CH2)(CH2PPh2)(pz)}(PMe3)] (3) was isolated. Complex 3 shows a unique fac coordination of the hybrid ligand with the allyl group eta(2)-bonded to the metal in the equatorial plane of a distorted trigonal bipyramid with one pyrazolate group remaining uncoordinated. This unusual feature can be rationalized on the basis of the electron-rich nature of the metal center. The related complex [Ir(CO){(pz)B(eta(2)-CH2CH=CH2)(CH2PPh2)(pz)}(PPh3)] (4) was found to exist in solution as a temperature-dependent equilibrium between the cis-pentacoordinated and trans square planar isomers with respect to the phosphorus donor atoms. Protonation of 3 with different acids is selective at the iridium center and gives the cationic hydrides [Ir{(allyl)B(CH2PPh2)(pz)(2)}(CO)H(PMe3)]X (X= BF4 (5), MeCO2 (6), and Cl (7)). Complex 7 further reacts with HCl to generate the unexpected product [Ir(CO)Cl{(Hpz)B(CH2PPh2)(pz)-CH2CH(Me)}(PMe3)]Cl (9; Hpz=protonated pyrazolyl group) formed by the insertion of the hydride into the Ir-(eta(2)-allyl) bond. In contrast, protonation of complex 4 with HCl stops at the hydrido complex [Ir{(allyl)B(CH2PPh2)(PZ)(2))(CO)H(PPh3)]Cl (8). X-ray diffraction studies carried out on complexes 2, 3, and 9 show the versatility of the hybrid scorpionate ligand in its coordination.