Iron‐ and Cobalt‐Catalyzed Synthesis of Carbene Phosphinidenes

Abstract

In the presence of stoichiometric or catalytic amounts of [M{N(SiMe 3 ) 2 } 2 ]( M = Fe,C o), N-heterocyclic carbenes (NHCs) react with primary phosphines to give as eries of carbene phosphinidenes of the type (NHC)·PAr. The formation of (IMe 4 )·PMes (Mes = mesityl) is also catalyzed by the phosphinidene-bridged complex [(IMe 4 ) 2 Fe-(m-PMes)] 2 ,w hichp rovides evidence for metal-catalyzed phosphinidene transfer.Transition-metal complexes of terminal phosphinidene ligands have stimulated considerable interest in recent years because of the fundamental interest in metal-phosphorus multiple bonds and because such complexes can serve as versatile organophosphorus reagents. [1][2][3][4][5] Complexes of the general type [L n M = PR] have been synthesized with many transition metals,and the ability of the phosphinidene ligand to display electrophilic or nucleophilic characteristics has enabled av ariety of phosphinidene-transfer reactions.W hile much of this chemistry was pioneered with 4d and 5d transition metals, [4,5] several important studies involving 3d metals have also been described. [6,7] Of particular significance is the three-coordinate nickel(II) phosphinidene complex [(dtbpe)Ni = P(C 6 H 3 -1,2-Mes 2 )] (dtbpe = di-tert-butylphosphinoethane,M es = mesityl), which is able to transfer the {PR} group to alkenes and alkynes in as toichiometric manner,t hus resulting in the formation of phosphorus heterocycles such as phosphiranes and phosphirenes. [6] Our interest in low-coordinate transition-metal chemistry has focused on iron and cobalt complexes of N-heterocyclic carbene (NHC) ligands. [8][9][10][11][12] NHC-stabilized iron and cobalt complexes of terminal or bridging phosphinidene ligands are currently unknown, hence we are interested in developing the phosphinidene-transfer chemistry of complexes of the type [(NHC) n M(PR)] (M = Fe,C o). We now report that NHCligated iron and cobalt phosphinidene complexes can indeed be synthesized, and they also show as trong tendency to couple the NHC to the phosphinidene group,w hich has allowed us to develop the first catalytic synthesis of carbene phosphinidenes,t hat is,c ompounds of the type (NHC)·PR.

Reactions of Low-Coordinate Cobalt(0)–N-Heterocyclic Carbene Complexes with Primary Aryl Phosphines

“…The phosphido ligand has a Co− P distance of 2.2254(9) Å that is comparable to those of the low-spin cobalt(I) phosphido complexes [Co(κ 3 -P-(CH 2 CH 2 PMe 2 ) 2 )(κ 2 -P(CH 2 CH 2 PMe 2 ) 3 )] (2.297(1) Å) 51 and Thomas' [(PPP)Co(CO) 2 ] (2.2386(6) Å) 52 and is apparently longer than those in the cobalt(III) phosphido complex 53 the cobalt terminal phosphinidene complex [(Cp)Co-(PPh 3 )(PMes*)] (2.1102(8) Å), 54 and the bridging phosphinidene complex [(IMe 4 ) 2 Co(PMes)] 2 (2.163(1) Å). 55 These metric data indicate the single bond nature of the Co−P interaction in 1. The IPr ligand has the short Co−C bond of 1.892(3) Å that is comparable to its counterparts in the reported low-spin cobalt(I)−NHC complexes having twolegged piano stool geometry, for example CpCo(IPr)(CO) (1.888(3) Å), 56 CpCo(IPr 2 H 2 )(PPh 3 ) (1.880(2) Å), 57 and Cp*Co(IPr)(CO) (1.902(5) Å).…”

NHCs in Main Group Chemistry

“…Formation of the (IMe 4 )PMes adduct is catalyzed also by the phosphinidene-bridged iron complex [(IMe 4 ) 2 Fe(μ-PMes)]. 813 The IMe 4 carbene reacts with the phosphaalkyne i Pr 2 NC P to yield the bicyclic P(I) complex 906. In contrast, reaction of IMe 4 with another phosphaalkene t BuCP and the reaction of i Pr 2 NCP with another NHC led to N-heterocyclic olefins (e.g., 907, Scheme 183).…”

N-Heterocyclic Carbene Complexes of Copper, Nickel, and Cobalt

“…The N(SiMe 3 ) 2 aminolysis strategy was further exemplified using the bis(silylamido) 29 Co to access the aryl-amido complexes 38 Co and 39a Co −39b Co , 563 and the phosphinidene complex 40 Co (Scheme 280). 564 Interestingly, a sequential substitution of the N(SiMe 3 ) 2 groups by NH(DiPP) anilido ligands is possible. Reaction of 29b uCo with 1 equiv NH 2 (DiPP) led to the mixed silylamide/aryl-amide complex 38 Co , while using an excess of NH 2 (DiPP) resulted in the formation of the symmetrical bis(anilido) complex 39a uCo .…”