STRUCTURAL AND CHEMICAL CHARACTERIZATION OF A PHOSPHINE BOUND M-H-M BRIDGED CARBONYLATE - ET4N+(MU-H)[MO2(CO)9PPH3]-

An X-ray crystal structure determination of Et4N+(μ-H)[Mo2(CO)9PPh3]- (1) has affirmed the positioning of PPh3 to be cis to the hydride bridge in a (bent, staggered) molecular anion framework. The compound crystallizes in the monoclinic space group P21/n with unit cell parameters of a = 16.386 (6) Å, b= 13.470 (5) Å, c = 17.085 (8) Å, and γ = 92.10 (7)° Pcalcd = 1-48 g cm-3 for Z = 4. The refinement led to a final R value of 0.034 based on 3518 observed reflections. The Mo-Mo separation is 3.4736 (7) Å, the bend of the molecular anion framework is 162.7°, the Mo-H-Mo angle is 127 (3)°, and the hydride is located asymmetrically between the Mo atoms, the shorter Mo-H distance (by 0.5 A) being to the Mo(CO)5 moiety. The quite long Mo-P bond (2.565 (1) Å) corroborated the solution chemistry of 1, which was kinetically dominated by a labile Mo-PPh3 bond. The kinetically determined Mo-P bond enthalpy in 1 is 23 ± 2.4 kcal/mol. The title compound may be used as precursor to more highly substituted dimer anions and/or neutral complexes, L2Mo(CO)4. © 1979, American Chemical Society. All rights reserved.