Binuclear Complexes with an Aminocarbene−Cyclopropenylidene Unit as Bridging Ligand:  Facile Migration of Carbonylmetal Fragments in Carbene Complexes

Abstract

The sequential reaction of the (dimethylamino)ethynylcarbene complexes [(CO)5MC(NMe2)C⋮CH] (1a−c: M = W (a), Mo (b), Cr (c)) with BuLi, [M(CO)6], and CF3SO3CH3 affords homobinuclear complexes with an aminocarbene−cyclopropenylidene bridging ligand, (3a−c). Two isomeric heterobinuclear complexes (4xy and 4yx) are formed in the reaction of [(CO)5MC(NMe2)C⋮CH] (1) with BuLi, [M‘(CO)6] (M ≠ M‘: W, Mo, Cr), and CF3SO3CH3. 4xy and 4yx differ in the relative distribution of the metals M and M‘: (4xy) and (4yx). The 4xy/4yx ratios obtained by the two different possible reaction sequences are similar. Complexes 4xy and 4yx do not interconvert. The reaction of cis-[(CO)4(Me3P)WC(NMe2)C⋮CH] with BuLi, [W(CO)6], and CF3SO3CH3 likewise gives two isomers, (7) and (8). These results demonstrate the facile migration of carbonylmetal fragments along a carbon chain. The structures of the complexes 3b,c and 7 have been established by X-ray structural analyses.

Recent advances in the field of multicarbene and multimetal carbene complexes of the Fischer-type

“…The proposed mechanism includes attack on a carbonyl ligand, migration of the metal fragment to the adjacent carbon atom and alkylation at the terminal oxygen atom [96]. Repeating the reactions with two different metal carbonyls yielded two isomers of the aminocarbene-cyclopropenylidene complex, where the two metal pentacarbonyl moieties had exchanged sites.…”

“…When applied in the area of Fischer carbene complexes of the type [M(CO) 5 {C(OR')R}], the carbene properties have either been modified by introducing metal-containing substituents to further activate the carbene carbon [65,96,98] or the carbene ligand is used as a connector to bridge the other transition metals [11,64,69,73,74]. In the ten years since Sierra's review article [11], very few applications of these multimetal complexes have been reported considering the interest in the cooperative mechanism of metals in catalytic transformations and the ability of the electropositive metals to effect modulation of reactive centres otherwise not possible by traditional organic fragments; and there is still little known about the reactivity of this type of Fischer carbenes.…”

Carbon–Carbon Bond Formation at a Neutral Terminal Carbido Ligand: Generation of Cyclopropenylidene and Vinylidene Complexes

“…C 3 (NiPr 2 ) 2 (5) [25] and in other cyclopropenylidene complexes. [9,[14][15][16][17][18][19][20][21][22][23] 2 Cl 2 ] similarly yields 2. In this case, too, 6 is not seen.…”

“…Unlike 3, however, the cyclopropenylidene units in these complexes are substituted by phenyl or electrondonating groups. [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23] [Ru(C)(H 2 IMes)(PCy 3 )Cl 2 ] (4; H 2 IMes = 4,5-dihydro-1,3-bis(mesityl)imidazol-2-ylidene) reacts similarly with DMAD, but the reaction is not clean since the product reacts further with DMAD before all of 4 has been consumed. However, 4 reacts more cleanly with HCCCO 2 Me (see the Supporting Information).…”

“…[6] The 13 C NMR shifts of the ring atoms in 3, 195.7 and 162.2 ppm, closely resemble those observed for 5 [25] but less so other cyclopropenylidene complexes, for which some cyclopropenium character is often invoked. [14][15][16][17][18][19][20][21][22][23] Unlike 1, 3 does not react appreciably with common olefins or alkynes, although under some conditions small amounts of 2 are formed, suggesting reversibility of the 2!3 transformation (see the Supporting Information). However, several reagents effect 1,1-addition of HX to the ring to form vinylidene complexes 7-10; reaction with pyridine-N-oxide similarly yields 11 (Scheme 1).…”