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

Abstract

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.

Unexpected Zwitterionic Allenyls from Silylenes and a Fischer Alkynylcarbene: A Remarkable Silylene‐Promoted Rearrangement

“…These results contrast with those previously known for reactions of phosphanes [20] and NHCs [16] with group 6m etal Fischer alkynyl(alkoxy)carbenes, which render products resulting from the simple conjugate addition of the nucleophile to the remote Ca tom (C g )o ft he alkynyl fragment (the phosphonium allenyl derivativesa re quite unstablei ns olution [20] ). SimilarC gaddition of nucleophiles has also been observed in reactions of less electrophilic Fischera lkynyl(aryl)carbenes of manganese [21] and rhenium. [22] Nucleophilic addition to the C a atom of Fischerc arbene complexes requires small and/or very strong (anionic) nucleophiles.…”

Protonation of manganese phosphonioallenyl complexes

“…A similar effect occurs in the parent allene complex Cp(CO) 2 Mn(h 2 -CH 2 ]C]CH 2 ) [15] and phosphinoallene complex C 5 H 4 Me(CO) 2 Mn(h 2 -Ph 2 PC(Ph)]C]C(Tol)H) [16], in which the metalecarbon distances are very close to those in 9. The coordinated C]C bond C(8)eC(9) ¼ 1.412(2) Å is longer than the uncoordinated C]C bond C(9)eC(10) ¼ 1.331(2) Å, these values being similar to those found in the allene manganese complexes [15,16] or phosphonioallene complexes of other metals [8ced,12]. The coordination causes the usually linear allene to bend away from the metal centre, the angle C(8)eC (9)eC(10) (144.82(16)) falls in the range of angles for h 2 -coordinated allenes (140e158 ) [11c,12: Table S1].…”

“…The MneC distance to the carbon atom bearing the PMePh 2 group MneC(8) ¼ 2.1282 (16) Å is significantly greater than that to the central carbon atom MneC(9) ¼ 2.0263(16) Å. A similar effect occurs in the parent allene complex Cp(CO) 2 Mn(h 2 -CH 2 ]C]CH 2 ) [15] and phosphinoallene complex C 5 H 4 Me(CO) 2 Mn(h 2 -Ph 2 PC(Ph)]C]C(Tol)H) [16], in which the metalecarbon distances are very close to those in 9.…”

“…The MneC distance to the carbon atom bearing the PMePh 2 group MneC(8) ¼ 2.1282 (16) Å is significantly greater than that to the central carbon atom MneC(9) ¼ 2.0263(16) Å. A similar effect occurs in the parent allene complex Cp(CO) 2 Mn(h 2 -CH 2 ]C]CH 2 ) [15] and phosphinoallene complex C 5 H 4 Me(CO) 2 Mn(h 2 -Ph 2 PC(Ph)]C]C(Tol)H) [16], in which the metalecarbon distances are very close to those in 9. The coordinated C]C bond C(8)eC(9) ¼ 1.412(2) Å is longer than the uncoordinated C]C bond C(9)eC(10) ¼ 1.331(2) Å, these values being similar to those found in the allene manganese complexes [15,16] or phosphonioallene complexes of other metals [8ced,12].…”

A Direct, Modular, and Efficient Construction of the PCP Structural Motif through Coupling of Manganese Carbyne Complexes with Phosphines

“…Though the key irreversible transformation [3 aa]BCl 4 ! [4 aa-H]BCl 4 may proceed through the stepwise formation of a manganese cis-hydride species by 1,3-H shift followed by reductive elimination, [6] the occurrence of a direct concerted 1,2proton migration from the phosphonium moiety to the ylidic carbon remains an alternate mechanistic possibility.Stepwise addition of molar equivalents of PPh 2 H followed by PCy 2 H to [1 Me ]BCl 4 at À80 8C led in the end to a mixture of two diphosphine complexes 4 aa and 4 ab in approximately 1:2.5 ratio (Scheme 1), finally isolated in 18 % and 49 % yield, respectively (see the Supporting information for details of the 4 aa/ Scheme 1. Coupling of [MpCMe)]BCl 4 with two equivalents of secondary phosphines (BCl 4 À anions omitted for clarity).…”