ADDITION, CYCLOADDITION, AND METATHESIS REACTIONS OF THE CATIONIC CARBYNE COMPLEXES [CP(CO)2MN-EQUIVALENT-TO-CCH2R]+ AND NEUTRAL VINYLIDENECOMPLEXES CP(CO)2M=C=C(H)R (M=MN, RE)

The cationic alkylidyne complexes [CP(CO)2M=CCH2R]+ (M=Re, R=H; M=Mn, R=H, Me, Ph) undergo facile deprotonation to give the corresponding ne utral vinylidene complexes CP(CO)2M=C=C-(H)R. For[CP(CO)2=CH3]+, this transformation occurs spontaneously at -78-degrees-C upon the addition of solvent (CH2Cl2 or THF) to the solid carbyne complex, but the mang anese complexes [Cp(CO)2-Mn=CCH2R]+(R=H,Me) require the addition of ex ternal base (e.g., Et3N) to induce their deprotonation. The manganese benzylcarbyne complex [CP(CO)2Mn=CCH2Ph]+ is intermediate in behavior. Except for CP(CO)2Mn=C=C(H)Ph, these vinylidene complexes are thermal ly unstable and must be generated and studied at low temperature. They are potent dipolarophiles which undergo net [2 + 2] cycloaddition wit h imines to give cyclic carbene complexes of the general form CP(CO)2M =CC(H)RC(H)PhN(R') (M = Re, R=H, R=Me, Ph; M=Mn, R'=Ph, R=H (17a), Me, Ph (17c)). Identical manganese products form upon treatment of the ma nganese carbyne complexes first with imine followed by addition of Et3 N. Permanganate oxidation of the manganese cyclic carbene complexes gi ves the corresponding beta-lactams in excellent yield. Also formed in the reactions of the rhenium complex CP(CO)2Re=C=CH2 with imines are t he products Cp(CO)2Re=CC(=C(H)Ph)C(H)PhN(R') (R'=Me, Ph (15b)), which have an exocyclic double bond formed via an aldol-type condensation be tween the initial cycloadduct and excess imine. The vinylidene complex es Cp(CO)2M=C=(H)R react with HN=C(Ph)2 to give imino-carbene complexe s of the general form CP(CO)2M=C(CH2R)N=C(Ph)2, which are derived by a ddition of the N-H bond across the vinylidene C=C bond. Similar produc ts form upon benzophenone imine addition to the manganese carbyne comp lexes, followed by addition of Et3N. Also formed in the reaction Of Cp (CO)2Mn=C=C(H)Ph or [CP(CO)2Mn=CCH2Ph]+ with HN=C(Ph)2 is the [2 + 2] cycloadduct Cp(CO)2Mn=CC(H)Ph-C(Ph)2N(H). Nitrile complexes, CP(CO)2Mn N=CCH2R, result from an organometallic analogue of the Beckmann rearra ngement upon treatment Of CP(CO)2Mn=C=C(H)R (R=H, Ph) or [CP(CO)2Mn=CC H2R]+(R=H,Me) with Ph2C=NNH2. Isocyanide complexes, CP(CO)2ReC=NR, are the result of reaction of the vinylidene complex CP(CO)2Re=C=CH2 with carbodiimides (RN=C=NR; R=Pr(i),Bu(t)), a reaction that proceeds via net metathesis of the vinylidene Re=C bond with the carbodiimide C=N b ond. A similar isocyanide product forms upon reaction Of [CP(CO)2Mn=CC H3]+ with Bu(t)N= C=NBu(t) and Et3N, and a C-13 labeling experiment in dicates a mechanism involving a 1,3-migration of the [CP(CO)2Mn] fragm ent in the intermediate [CP(CO)2MnC(=CH2)N(Bu(t))=C=N(Bu(t))]. Reactio n of both [CP(CO)2Mn=CCH3]+ and CP(CO)2Mn=C=CH2 with Pr(i)N=C=NPr(i) g ave the ansa-carbene complex {eta5-C5H46(=CH2))(CO)2Mn=C(N(H)Pr(i))(NP r(i)) (41) by a path involving a similar 1,3-migration of the [CP(CO)2 Mn] fragment and insertion of the original vinylidene or carbyne alpha -carbon into the one of the C-H bonds of the cyclopentadienyl ligand. A by product of this reaction is the bis(amino)carbene complex {eta5-C 4H5-C(O)CH3(CO)2Mn=C(NHPr(i))2 (45), with an acetyl substituent on the cyclopentadienyl ligand, a product that likely results from hydrolysi s of the above-mentioned ansa-carbene complex. The unusual zwitterioni c vinylidene complex CP(CO)2Mn=C=C(Me)CN(Bu(t))B-Cl2N+(Bu(t)) (46) is the principal product of the reaction of the propylidyne complex [CP(C O)2Mn=CCH2Me]+ with Bu(t)N=C=NBu(t) and Et3N. With benzalazine, Ph(H)C =NN=C(H)Ph, the complexes CP(CO)2Re=C=CH2 and [CP(CO)2-Mn=CCH3]+ react to form the bimetallic bis(carbene) complexes CP(CO)2M=CC(H)2C(H)PhNN C(H)-PhC(H)2C=M(CO)2Cp (M=Re, Mn (47)), which result from consecutive [3 + 2] cycloaddition reactions of the azine with 2 equiv of the organ ometallic reagents. Crystal structures are reported for 15b, 17a, 41, 45, 46, 47, and the eta5-C5H4Me analogue of 17c.