| 15852111 |
Ortin Y, Lugan N, Mathieu R: Subtle reactivity patterns of non-heteroatom-substituted manganese alkynyl carbene complexes in the presence of phosphorus probes. Dalton Trans. 2005 May 5;(9):1620-36. Epub 2005 Apr 1.
The non-heteroatom-substituted manganese alkynyl carbene complexes (eta5-MeC5H4)(CO) 2Mn=C (R) C [triple bond] 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 [eta5-MeC5H4)(CO) 2Mn [triple bond] CR][BPh4]([2][BPh4]) with the appropriate alkynyllithium reagents LiC [triple bond] 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 (eta5-MeC5H4)(CO) 2Mn=C (Tol) C [triple bond] CPh (3c), and its precursor [(eta5-MeC5H4)(CO) 2Mn=CTol][BPh4]([2b](BPh4]) are reported. The reactivity of complexes toward phosphines has been investigated. In the presence of PPh3, complexes act as a Michael acceptor to afford the zwitterionic sigma-allenylphosphonium complexes (eta5-MeC5H4)(CO) 2MnC (R)=C=C (PPh3) 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 (eta5-MeC5H4)(CO) 2MnC (Ph)=C=C (PPh3) Tol (5b) support the proposal. In the presence of PMe3, complexes undergo a nucleophilic attack on the carbene carbon atom to give zwitterionic sigma-propargylphosphonium complexes (eta5-MeC5H4)(CO) 2MnC (R)(PMe3) C [triple bond] CR' (6). Complexes 6 readily isomerise in solution to give the sigma-allenylphosphonium complexes (eta5-MeC5H4)(CO) 2MnC (R')=C=C (PMe3) R (7) through a 1,3 shift of the [(eta5-MeC5H4)(CO) 2Mn] fragment. The nucleophilic attack of PPh2Me on 3 is not selective and leads to a mixture of the sigma-propargylphosphonium complexes (eta5-MeC5H4)(CO) 2MnC (R)(PPh (2) Me) C [triple bond] CR' (9) and the sigma-allenylphosphonium complexes (eta5-MeC5H4)(CO) 2MnC (R)=C=C (PPh (2) Me) R' (10). Like complexes 6, complexes 9 readily isomerize to give the sigma-allenylphosphonium complexes (eta5-MeC5H4)(CO) 2MnC (R')=C=C (PPh2Me) R'). Upon gentle heating, complexes 7, and mixtures of 10 and 10' cyclise to give the sigma-dihydrophospholium complexes (eta5-MeC5H4)(CO) 2MnC=C (R') PMe2CH2CH (R)(8), and mixtures of complexes (eta5-MeC5H4)(CO) 2MnC=C (Ph) PPh2CH2CH (Tol)(11) and (eta5-MeC5H4)(CO) 2MnC=C (Tol) PMe2CH2CH (Ph)(11'), respectively. The reactions of complexes 3 with secondary phosphines HPR (1)(2)(R1= Ph, Cy) give a mixture of the eta2-allene complexes (eta5-MeC5H4)(CO) 2Mn [eta2-{R (1)(2) PC (R)=C=C (R') H}](12), and the regioisomeric eta4-vinylketene complexes [eta5-MeC5H4)(CO) Mn [eta4-{R (1)(2) PC (R)=CHC (R')=C=O}](13) and (eta5-MeC5H4)(CO) Mn [eta4-{R (1)(2) PC (R')=CHC (R)=C=O}](13'). The solid-state structure of (eta5-MeC5H4)(CO) 2Mn [eta2-{Ph2PC (Ph)=C=C (Tol) H}](12b) and (eta5-MeC5H4)(CO) Mn [eta4-{Cy2PC (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. |
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