Syntheses, Structures and Spectroscopic Studies of Dimolybdenum Complexes Containing Bridging Butyrate and Phosphine Ligands

By reactions of Mo 2 (O 2 CPr n )X 2 (PPh 3 ) 2 (X = Cl, 1 ; X = Br, 2 ) with Ph 2 PCH 2 CH 2 P(Ph)CH 2 CH 2 PPh 2 (etp) in CH 2 X 2 , the quadruply bonded complexes containing bridging butyrate and tridentate phosphine ligands of the type Mo 2 (O 2 CPr n )X 3 (η 3 ‐etp) (X = Cl, 3 ; X = Br, 4 ) were prepared. Their UV‐vis and 31 P{ 1 H}‐NMR spectra have been recorded and the structures of 1 and 2 have been determined by X‐ray crystallography. Crystal data for 1 : space group P2 1 /c, a = 9.708 (2)Å, b = 18.491 (4)Å, c= 12.688 (3)Å, β = 110.76 (3)°, V = 2130 Å 3 , Z = 2, with final residuals R = 0.0441 and Rw = 0.0519. Crystal data for 2 : space group P2 1 /c, a = 9.737 (1)Å, b = 18.632(1)Å, c = 12.680(1)Å, β= 110.27 (1)°,V = 2158.2 (3) Å 3 , Z = 2, with final residuals R = 0.0322 and Rw = 0.0481. The δ → δ* transition energies, 31 P{ 1 H}‐NMR chemical shifts and the coupling constants are dependent on the natures of the halogen atoms and the carboxylate ligands. The through metal‐metal couplings | 3 J P‐Mo‐Mo‐P | for complexes of the type Mo 2 (O 2 CR)X 3 (η 3 ‐P 3 ), which contain η 3 ‐polydentate phosphine ligands are about 20 ± 2 Hz.