REACTION OF (DIBENZOPHOSPHOLYLLITHIUM)PENTACARBONYLMOLYBDENUM WITH PROPARGYL BROMIDE - SYNTHESIS AND STRUCTURAL CHARACTERIZATION OF A TETRACARBONYLMOLYBDENUM COMPLEX OF AN UNSYMMETRICAL CIS-BIS(DIBENZOPHOSPHOLYLETHENE)

Lithium dibenzophospholide (LiDBP) reacts with MO(CO)6 in tetrahydrofu ran to produce (DBPLi)Mo(CO)5 (1). Compound 1 reacts with H+, BrCH2C=C H, and BrCH2CH2Br to produce (HDBP)Mo(CO)5, (2), (H-C=C-CH2DBP)Mo(CO)5 , (3), and the dimer [(CO)5Mo(DBP)]2, (4), which contains a phosphorus -phosphorus bond, respectively. Compound 2 undergoes a pyridine promot ed phosphorus-hydrogen addition to the carbon-carbon triple bond of co mpound 3 to produce (CO)5Mo[DBP-CH2-C(=CH2)DBP]Mo(CO)5, (5), which und ergoes a thermal 1,3-hydrogen migration and Mo(CO)6 elimination to pro duce cis-[DBPCH=C(CH3)DBP]Mo(CO)4, (6). These compounds have been char acterized by elemental analyses, infrared and H-1, C-13 {H-1}, P-31 {H -1} and Mo-95 NMR spectroscopy. The structures of 5 and 6 have been de termined from three-dimensional X-ray data collected by counter method s. Compound 5 crystallized in the space group P1BAR with a = 12.010 (4 ) angstrom, b = 12.557 (3) angstrom, c = 13.174 (3) angstrom, alpha = 104.67 (2)degrees, beta = 101.10 (2)degrees, gamma = 93.54 (2)degrees, U = 1 873.2 (8) angstrom3; and Z = 2. Compound 6 crystallized in the space group P2(1)/n with a = 9.001 (3) angstrom, b = 20.090 (11) angst rom, c = 15.407 (7) angstrom, beta = 94.19 (3)degrees, U = 2 779 (2) a ngstrom3 , and Z = 4. The structures were refined by least-squares met hods with R = 0.038 for 5 and R = 0.064 for 6 for 5 086 and 3 662 uniq ue reflections with I/sigma(I) greater-than-or-equal-to 2.0. The Mo-P distances (2.514 (1), 2.507 (1) angstrom) are slightly different in 5 and both are longer than those (2.463 (4), 2.474 (4) angstrom) in 6. T he shorter Mo-P distances in 6 are the combined result of diminished s teric interactions, the chelate effect, and the greater pi-acceptor ab ility of the ligand.