OXIDATIVE ADDITION OF A P-O-P LINKAGE AND METAL METAL BOND FORMATION ACROSS A DIMOLYBDENUM CAGE

The dimolybdenum cage complex Mo(CO)4[iPr2NPO]4Mo(CO)4 was reacted with tertiary phosphines of the type PPh2R (R = Ph, Me, H) in refluxing toluene. In each case, incorporation of a single phosphine led to the loss of three carbonyls to form orange complexes of the type Mo(CO)3[iPr2NPO]4Mo(CO)2PPh2R (1a, 1b, 1c). One- and two-dimensional P-31 NMR spectroscopy suggested substantial alterations of the parent adamantanoid cage structure upon CO replacement. By contrast, substitutions using trimethyl phosphite under milder conditions yielded both mono- and disubstituted products: Mo(CO)4-[iPr2NPO]4Mo(CO)3P(OMe)3 (2) and Mo(CO)3P(OMe)3[iPr2NPO]4Mo(CO)3P(OMe)3 (3) with the original core structure intact. The former can be shown by P-31 COSY NMR spectroscopy to be a mixture of fac- and mer-substituted diastereomers. The latter was found to be a mixture of all four disubstituted diastereomers. Upon further heating, both of these transformed to orange-red Mo(CO)3[iPr2NPO]4Mo(CO)2P(OMe)3 (1d) an analogue of complexes 1a-1c. The X-ray molecular structure of 1d has been determined. Crystal data: monoclinic, P2(1)/n, a = 13.026 (3) angstrom, b = 21.054 (3) angstrom, c = 18.118 (3) angstrom, beta = 103.46 (2)-degrees, V = 4832 (2) angstrom 3, Z = 4, final R = 0.042, and R(w) = 0.044 for 6070 reflections and varying 497 parameters. This revealed that a cage P-O-P bond has been cleaved near the substitution site with the resulting phosphinito oxygen replacing a second CO. Additionally, the phosphido group generated displaced a third CO at the other Mo center to bridge the two metals which are now within bonding distance (3.173 (1) angstrom) of each other. Similar reactions using pyridine also produced a related orange-red product, Mo(CO)3[iPr2NPO]4Mo(CO)2NC5H5 (1e). This pyridine ligand is readily displaced by CO gas to generate Mo(CO)3[iPr2NPO]4Mo(CO)3 (1f). The X-ray structure of 1f has also been determined. Crystal data: monoclinic, C2/c, a = 36.523 (7) angstrom, b = 13.287 (5) angstrom, c = 20.348 (3) angstrom, beta = 109.48 (1)-degrees, V = 9310 (4) angstrom 3, Z = 8, final R = 0.055, and R(w) = 0.074 for 4723 reflections and 452 variables. A similar polycyclic core structure to 1d was found. Intermediates similar to 2 and 3 can be isolated in low yields from the PPh2H reaction at below 100-degrees-C.