Subtle reactivity patterns of non-heteroatom-substituted manganese alkynyl carbene complexes in the presence of phosphorus probes

摘要

The non-heteroatom-substituted manganese alkynyl carbene complexes(eta~5-MeC_5h_4)(CO)_2Mn=C(R)C=CR'(3;3a:R=R'=Ph,3b:R=Ph,R'=Tol,3c:R=Tol,R'=Ph)have been synthesised in high yields upon treatment of the corresponding carbyne complexes [(eta~5-MeC_5h_4)(CO)_2Mn=CR]rBPh_4]([2][BPh_4])with the appropriate alkynyllithium reagents LiC=CR'(R'=Ph,Tol).The use of tetraphenylborate as counter anion associated with the cationic carbyne complexes has been decisive.The X-ray structures of(eta~5-MeC_5h_4)(CO)_2Mn=C(Tol)C=CPh(3c),and its precursor [(eta~5-MeC_5h_4)(CO)_2Mn=CTol][BPh_4]([2b](BPh_4])are reported.The reactivity of complexes 3 toward phosphines has been investigated.In the presence of PPh_3,complexes 3 act as a Michael acceptor to afford the zwitterionic sigma-allenyl-phosphonium complexes(eta~5-MeC_5h_4)(CO)_2MnC(R)=C=C(PPh_3)R'(5)resulting from nucleophilic attack by the phosphine on the remote alkynyl carbon atom.Complexes 5 exhibit a dynamic process in solution,which has been rationalized in terms of a fast [NMR time-scale] rotation of the allene substituents around the allene axis;metrical features within the X-ray structure of(eta~5-MeC_5h_4XCO)_2MnC(Ph)=C=C(PPh_3)Tol(5b)support the proposal.In the presence of PMe_3,complexes 3 undergo a nucleophilic attack on the carbene carbon atom to give zwitterionic sigmsigma-propargylphosphonium complexes(eta~5-MeC_5h_4)(CO)_2MnC(R)(PMe_3)C=CR'(6).Complexes 6 readily isomerise in solution to give the sigma-allenylphosphonium complexes(Tf-MeC_5h_4)(CO)_2MnC(R')=C=C(PMej)R(7)through a 1,3 shift of the [(eta~5-MeC_5h_4)(CO)_2Mn] fragment.The nucleophilic attack of PPh_2Me on 3 is not selective and leads to a mixture of the cr-propargylphosphonium complexes(eta~5-MeC_5h_4)(CO)_2MnC(R)(PPh_2Me)C=CR'(9)and the sigma-allenylphosphonium complexes(eta~5-MeC_5h_4)(CO)_2MnC(R)=C=C(PPh_2Me)R'(10).Like complexes 6,complexes 9 readily isomerize to give the sigma-allenylphosphonium complexes(eta~5-MeC_5h_4)(CO)_2MnC(R')=C=C(PPh_2Me)R(10).Upon gentle heating,complexes 7,and mixtures of 10 and 10'cyclise to give the sigma-dihydrophospholium complexes(Tl5-MeC_5h_4)(CO)_2MnC=C(R')PMe_2Ch_2CH(R)(8),and mixtures of complexes(if-MeC_5h_4)(CO)_2MnC=C(Ph)-PPh_2Ch_2CH(Tol)(11)and(eta~5-MeC_5h_4)(CO)_2MnC=C(Tol)PMe_2Ch_2CH(Ph)(11),respectively.The reactions of complexes 3 with secondary phosphines HPR_2~1(R1=Ph,Cy)give a mixture of the eta~2-allene complexes(eta~5-MeC_5h_4)-(CO)_2Mn[eta~5-{R_2~1PC(R)=C=C(R')H}](12),and the regioisomeric eta~2-vinylketene complexes(eta~5-MeC_5h_4)(CO)Mn-[ETA~4-{R_2~1PC(R)=CHC(R')=C=O}](13)and(eta~5-MeC_5h_4)(CO)Mn[eta~4-{R_2~1PC(R')=CHC(R)=C=O}](13).The solid-state structure of(eta~5-MeC_sh_4XCO)_2Mn[eta~5-{Ph_2PC(Ph)=C=C(Tol)H}](12b)and(eta~5-MeC_5h_4)(CO)Mn[T14-{Cy_2PC(Ph)=CHC(Ph)=C=O}](13d)are reported.Finally,a mechanism that may account for the formation of the species 12,13 and 13'is proposed.