Complex chemistry of reactive organic compounds. 28. Carbene addition to metal carbonyls - a novel reaction in organometallic chemistry. Direct synthesis of .eta.2-ketene complexes from diazoalkanes

Abstract

Communications to the Editor 3133 (10) An approximate covalent radius of Fe(0) pertinent to the present situation is taken as one half of the average Fe-Fe distance in the triply bridged compounds Fe2(CO)9 (2.523 (1) A)11 and NaHFe2(CO)8 (2.521 (1) A).12 An appropriate value for silver is the Pauling tetrahedral radius of 1.44 A.

A new mechanism of nucleophilic vinylic substitution and unexpected products in the reaction of chlorotrifluoroethylene with [Re(CO)5]Na and [CpFe(CO)2]K

“…Moreover, if we consider that carbenes (and consequently carbenoids) are easily inserted into metal-C"O bond [16], formation of metalacycle XI from the carbenoid anion A-Fe can be also explained. Insertion of the carbene equivalent into Fe-C"O bond will produce the iron ketene complex C (Scheme 15).…”

Reductive Cleavage of Carbon Monoxide by a Disilenide

“…Thef ormal addition product 2 of four equivalents of CO to two molecules of 1 was isolated as ap ale yellow solid by crystallization from hexane at room temperature in 82 %yield (Scheme 1). [20] The 29 Si NMR spectrum of 2 shows four resonances at d = À9.14, À29.50, À45.63, and À98.33 ppm, in line with the four chemically inequivalent Si atoms in compound 2 (Scheme 1). Thes ignal at the highest field is in the typical region for 1-silacyclopropenes (silirenes).…”

“…[20] Thel iberated ketenylidene donor site intramolecularly coordinates to the silylene moiety instead. Thei sonitrile complex 7d exhibited 29 Si NMR shifts at + 55.78 ppm ( 1 J SiÀW = 116 Hz) and (4) ) is significantly shorter than Si1-C1 (1.961(4) ), suggesting that Si1 retains ac ertain silylene character.T his is reminiscent of the observation by Bacereido et al that aphospha ylidic ketenyl moiety,ifatall, interacts only very weakly with aLewis acidic boryl group in b position. [33] Conversely,the reaction of 6c with one equivalent of aNheterocyclic carbene (NHC Me 4 = 1,3,4,5-tetramethylimidazol-2-ylidene) resulted in the coordination of the NHC Me 4 to the donor-free silylene ligand, affording 8 in near quantitative yield as ap ale-yellow crystalline material (Scheme 4).…”

“…[28] Manganese carbonyls are known to convert into h 2 -ketene complexes by reaction with carbene precursors. [29] Notably,e ven surface carbide species on Fischer-Tropsch catalysts have been proposed to form CCO fragments in the presence of CO. [30] On this basis,w e Angewandte decided to investigate the reactivity of disilenide 1 toward Group 6m etal hexacarbonyls,w hich could not only stabilize apostulated intermediate,but would also supply the required two equivalents of CO.Indeed, the reaction of 1 with M(CO) 6 (M = Cr,M o, W) in benzene initially resulted in uniform products in all three cases.A nX -ray diffraction study on single crystals of the tungsten derivative (see below) allowed the identification of the series as h 1 -ketenyl-functionalized silylene complexes 6a-c (Scheme 3). [20] Thedonor-free silylene centers in complexes 6a-c showed diagnostic signals [31] in the 29 Si NMR spectra at + 320.39 (6a; M = Cr), + 313.01 (6b;M= Mo), and + 296.11 ppm (6c;M= W; 1 J SiÀW = 138 Hz).…”

“…Thea nionic ketenyl moiety coordinates to tungsten at aW 1-C1 distance of 2.375(4) , which is significantly longer than reported W À C ketene bond lengths, [32] suggesting arelatively weak interaction as aresult of the geometric constrains of the metallacycle.C 1i so nly slightly pyramidal with AEC1 = 358.988 8,which hints to acertain ynolate character of the ketenyl unit, comparable to the resonance structure [4' '] of the postulated intermediate of the formation of 2.Indeed, the angle Si2-C1-C2 is with 129.8(4)8 8 significantly wider than the ideal 1208 8 expected for sp 2 hybrids,a lthough, the C1-C2 and C2-O2 distances in 6c of 1.270(6) a nd 1.189 (6) , respectively,f all within the range of reported double bonds of ketenes. [32] Thef ormation of the silylene complexes 6a-c can be rationalized by invoking precisely the same anionic intermediates as postulated in the mechanism for the generation of 2.T he Group 6m etal centers can reasonably be expected to stabilize the transient silylenoid [3] to such an extent that Si(Tip) 2 extrusion becomes unfavorable.I nstead, cyclization of the ligand system to [5] followed by insertion of the coordinatively unsaturated metal center into the adjacent Si-C ketenyl bond would give 6a-c.H owever, in [D 6 ]benzene,t he silylene complexes 6a-c slowly convert into more stable complexes 7a-c with strongly high-field-shifted 29 Si NMR resonances (7a: + 75.74, À21.82; 7b: + 66.97, À22.18; 7c: + 48.71, À21.70 ppm) accompanied by the formation of an insoluble black residue (Scheme 3). Thechromium derivative crystallized from hexane as olive-colored crystals in 48 % yield.…”