INTERACTION OF ETHYNYLIRON (FP-C-EQUIVALENT-TO-C-H AND FP-ASTERISK-C-EQUIVALENT-TO-C-H) AND ETHYNEDIYLDIIRON COMPLEXES (FP-ASTERISK-C-EQUIVALENT-TO-C-FP-ASTERISK) WITH CO2(CO)8 - FORMATION OF A CLUSTER COMPOUND WHICH IS FLUXIONAL VIA A METAL METAL BOND SCISSION AND RECOMBINATION PROCESS

Interaction of ethynyliron complexes Fp-C=C-H (1) and Fp*-C=C-H (2) with Co2(CO)8 in THF results in the respective formation of the expected deep green adducts with a tetrahedral C2CO2 core, Co2(CO)6(mu-eta-2:eta-2-M-C=C-H) (3, M = Fp; 4, M = Fp*). The structural features of 3 and 4 characterized by spectroscopic (and crystallographic) analyses are essentially the same as those of adducts derived from normal alkynes, Co2(CO)6(mu-eta-2:eta-2-R-C=C-R'). The reaction of the ethynediyldiiron complex Fp*-C=C-Fp* (7) with CO2(CO)8 similarly affords the deep green adduct Cp*Fe[Co(CO)2]2(mu-CO)2(mu-eta-1:eta-2:eta-2-C=C-Fp*) (8), which turns out to be fluxional at ambient temperature. The crystallographic analysis has revealed that the C2 ligand in 8 binds the four metal atoms together in a mu-4-eta-1(Fe):eta-1-(Fe):eta-2(Co):eta-2(CO) fashion; in other words, the bridging C2 ligand interacts with a remote iron atom in an eta-1(sigma) fashion and with the remaining FeCO2 cluster part in a mu-3-eta-1(Fe):eta-2(Co):eta-2(Co) fashion, respectively. A rare example of fluxional behavior of 8 via a metal-metal bond scission and recombination process has been studied by variable-temperature C-13 NMR analyses, and below -60-degrees-C spectra consistent with the solid-state structure have been obtained. Crystal data: 3, triclinic, space group P1BAR, Z = 2, a = 9.798 (1) angstrom, b = 13.082 (3) angstrom, c = 7.765 (1) angstrom, alpha = 95.06 (2)-degrees, beta = 114.10 (1)-degrees, gamma = 97.54 (2)-degrees, V = 889.5 (3) angstrom3, R (R(W)) = 0.050 (0.043) for 2632 reflections with I > 3-sigma-(I); 8, monoclinic, space group C2/c, Z = 8, a = 33.095 (9) angstrom, b = 10.131 (3) angstrom, c = 20.572 (7) angstrom, beta = 113.19 92)-degrees, V = 6340 (4) angstrom-3, R (R(W)) = 0.081 (0.071) for 1524 reflections with I > 3-sigma-(I).