ic8011958_si_001.cif (67.35 kB)

Four-Coordinate Mo(II) as (silox)2Mo(PMe3)2 and Its W(IV) Congener (silox)2HW(η2-CH2PMe2)(PMe3) (silox = tBu3SiO)

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posted on 17.11.2008, 00:00 by David S. Kuiper, Peter T. Wolczanski, Emil B. Lobkovsky, Thomas R. Cundari
The reduction of [(tBu3SiO)2MoCl]2 (22) provided the cyclometalated derivative, (silox)2HMoMo(κ-O,C-OSitBu2CMe2CH2)(silox) (3), and alkylation of 22 with MeMgBr afforded [(tBu3SiO)2MoCH3]2 (42). The hydrogenation of 42 was ineffective, but the reduction of 22 under H2 generated [(tBu3SiO)2MoH]2 (52), and the addition of 2-butyne to 3 gave [(silox)2Mo]2(μ:η2η2-C2Me2) (6), thereby implicating the existence of [(silox)2Mo]2 (12). The addition of (silox)H to Mo(NMe2)4 led to (silox)2Mo(NMe2)2 (7), but further elaboration of the core proved ineffective. The silanolysis of MoCl5 afforded (silox)2MoCl4 (8) and (silox)3MoCl3 (9) as a mixture from which pure 8 could be isolated, and the addition of THF or PMe3 resulted in derivatives of 9 as (silox)2Cl3MoL (L = THF, 10; PMe3, 11). Reductions of 11 and (silox)2WCl4 (15) in the presence of excess PMe3 provided (silox)2Cl2MPMe3 (M = Mo, 12; W, 16) or (silox)2HW(η2-CH2PMe2)PMe3 (14). While “(silox)2W(PMe3)2” was unstable with respect to W(IV) as 14, a reduction of 12 led to the stable Mo(II) diphosphine, (silox)2Mo(PMe3)2 (17). X-ray crystal structures of 10 (pseudo-Oh), 12 (square pyramidal), and 14 and 17 (distorted Td) are reported. Calculations address the diamagnetism of 12 and 16, and the distortion of 17 and its stability to cyclometalation in contrast to 14.