SYNTHESIS AND CHARACTERIZATION OF (CP)2MO2(CO)4(MU-ETA-2-ETA-2-FP-C=C-H), ADDUCTS OF ETHYNYLIRON COMPLEXES TO (CP)2MO2(CO)4 - THEIR FLUXIONAL BEHAVIOR VIA REVERSIBLE 1-ALKYNE-VINYLIDENE LIGAND INTERCONVERSION ON A DINUCLEAR SYSTEM AND PHOTOCHEMICAL DECARBONYLATION LEADING TO THE MU-3-VINYLIDENYL COMPLEXES (CP)FECP2MO2(CO)4(MU-CO)(MU-=C=CH)

Interaction of the ethynyliron complexes FP-C=C-H (1) with (CP)2Mo2(CO)4 (2) affords the adducts (CP)2Mo2(CO)4(mu-eta2:eta2-FP-C=C-H) (3) with the tetrahedral C2Mo2 core in a manner similar to the reaction of alkynes. Although the molecular structures Of Cp2Mo2(CO)4-(mu-eta2:eta2-Fp-C=C-H) (3a) and CP2Mo2(CO)4(mu-eta2:eta2-Fp(Si)-C=C-H) (3e) are close to those of normal alkyne adducts with the exception of the Mo-C(Fe) distances being slightly longer than the Mo-C(H) distances, 3 shows complicated dynamic behavior. Variable-temperature C-13 NMR analyses of 3 have revealed two characteristic features: (1) The two sharp C2H doublets observed at low temperature broaden in the medium-temperature range and finally appear as two signals at the fast-exchange limit. This behavior is interpreted in terms of a reversible 1,2-H migration mechanism via the vinylidene intermediate (CP)2Mo2(CO)4[mu-eta1:eta2-C=C(H)FP] (C). (2) All the Mo-CO's are observed equivalently at higher temperature via an undetermined process. Irradiation of 3a,b results in decarbonylation to give the isomeric mixture Of mu3-vinylidenyl complexes (CP)FeCP2Mo2(CO)4(mu-CO)(mu3-C2H) with an Mo-Mo-Fe linkage (5a, CP = Cp; 5b, CP = Cp*). The structure of 5a determined crystallographically is described as the dimolybdenum mu-eta1:eta2-vinylidene complex Mo2(mu-eta1:eta2=C=CR2) bearing an Fe group as one of the vinylidene substituents (R). The formation and the structure of 5a support C. Crystal data: 3a, C23H16O6FeMo2, space group P2(1)/a (monoclinic), a = 18.318(2) angstrom, b = 9.709(2) angstrom, c = 12.608(3) angstrom, beta = 98.85(1)-degrees, V = 2216(1) angstrom3, Z = 4, R (R(w)) = 0.044 (0.039); 3e, C26H24O6SiFeMo2, space group P2(1)/c (monoclinic), a = 12.608(2) angstrom, b = 23.224(12) angstrom, c = 9.172(2) angstrom, beta = 96.11(2)-degrees, V = 2670(3) angstrom3, z = 4, R (R(w)) = 0.051 (0.056); 5a, C22H16O5FeMo2, space group P2(1)/a (monoclinic), a = 15.197(3) angstrom, b = 17.362(5) angstrom, c = 8.080(3) angstrom, beta = 101.32(2)-degrees, V = 2090(1) angstrom3, z = 4, R (R(w)) = 0.046 (0.039).