HYDRODEMETALATION OF ALKYNES AND DIYNES - DIIRON COMPLEXES OF MU-ETA-1-ETA-2-ALKENYL LIGANDS WITH PENDANT ALKYNES - CRYSTAL AND MOLECULAR-STRUCTURE OF FE2(CO)6(MU-PPH2) (MU-2-ETA-1-ETA-2-CH = CH2) AND FE2(CO)6(MU-PPH2)(MU-2-ETA-1-ETA-2-C(C-EQUIVALENT-TO-CME) = CHME)

The reactions of alkynes and diynes with HFe2(CO)7(mu-PPh2) gives the bridging alkenyl complexes Fe2(CO)6(mu-PPh2)(mu-eta1:eta2-R2C=CHR1). In the case of alkynes R1C=CR2 (R2 = TMS, H, Ph, OEt, CH2Cl, and R1 = H, or R2 = R1 = Ph) bydrodimetalation affords a single major isomer in which the stereochemistry of the substituents on the original unsaturated organic substrate is cis. There is also a high regiospecificity of reaction leading to gem dihydrides in the final products. The X-ray structure of the parent vinyl complex Fe2(CO)6(mu-PPh2)(mu2-eta1:eta2-CH=CH2) (5) has been determined. Crystals of 5 are monoclinic, space group P2(1)/c, with a = 14.695 (4) angstrom, b = 11.410 (2) angstrom, c = 12.163 (3) A, beta = 92.90 (2) angstrom, V = 2037.5 (8) angstrom3, and Z = 4. Refinement converged at R = 0.028 and R. = 0.027 on the basis of 2902 observed reflections. A similar procedure was used to prepare the first diiron alkenyl complexes Fe2(CO)6(mu-PPh2)(mu-eta1:eta2-R2C=CHR1) [R1 = Ph, H, Me and R2 = C=CPh, CrH4C=CH, C=CMe] containing the pendant unsaturated functionalities, C=CR. The structure of Fe2(CO)6(mu-PPh2)(mu-eta1:eta2-C(C=CMe)=CHMe) has been determined by single-crystal X-ray diffraction studies. This compound crystallises in the monoclinic space group P2(1)/n with a = 10.966 (2) angstrom, b = 13.082 (3) angstrom, c = 16.180 (2) angstrom, beta = 90.35 (1)-degrees, V = 2320.6 (8) angstrom3, and Z = 4. Refinement converged at R = 0.028 and R(w) = 0.033 on the basis of 4397 observed reflections. The molecule Fe2(CO)6(mu-PPh2) (mu-eta1:eta2-C(C=CMe)=CHMe) contains an yne-enyl ligand resulting from regiospecific hydrodimetalation at the diyne substrate (MeC=CC=CMe). In the major isomer the pendant unsaturated moiety is found on C(alpha). The variable temperature C-13{H-1} NMR spectra of 5 revealed dynamic behavior involving three independent processes: two low-energy trigonal rotations of vastly disparate energies, and a much higher energy process involving equilibration of the two nonequivalent tricarbonyl iron sites.