REACTION BETWEEN BENZOPHENONE AND DITUNGSTEN HEXAALKOXIDES - MOLECULAR-STRUCTURE AND REACTIVITY OF W(OCH2-TERT-BU)4(PY)(ETA-2-OCPH2)

Reactions of W2(OR)6(py)2 (R = OCH2-t-Bu, 0-i-Pr) with benzophenone are shown to produce a mixture of products, including W(OR)4(py)(Ph2CO), W(OR)4(OCPh2CPh2O), one containing a terminal alkylidene (W=CPh2), Ph2CCPh2, and Ph2CHCHPh2. The X-ray crystal structure of W(OCH2-t-Bu)4(py)(Ph2CO) has been determined and found to contain a highly reduced, asymmetrically bonded benzophenone ligand; W-O = 1.970 (6) Å, W-C = 2.234 (10) Å, and C-O = 1.397 (11) Å. Crystal data for W(OCH2-t-Bu)4-(py)(Ph2CO) at -144 °C: a = 15.675 (1) Å, b = 13.736 (1) Å, c = 17.936 (2) Å, β = 92.39 (1)°, Z = 4, dcalc = 1.365 g cm-3, and space group p21/c. Reactions of W2(OR)6 (R = OCH2-t-Bu, O-c-C6H11) with benzophenone produce tetraphenylethane as the only organic product. Labeling studies show the H atoms of tetraphenylethane are primarily from the alkoxide ligands. A mechanism for these reactions based on an intermediate ?-diphenylalkylidene compound is proposed. © 1990, American Chemical Society. All rights reserved.