Formation of C−C, C−N, and C−O Links between Isonitrile, Cyclopentadienyl, and Hydroxide Ligands Bound to Molybdenum(III): Syntheses and Crystal Structures of μ-Aminocarbyne and μ-Amino-oxycarbene Dimolybdenum Complexes
Résumé
Reaction of the bis- isonitrile complex [Mo2Cp2(mu-SMe)(3)(xylNC)(2)](BF4) (2b) with NaOH (suspension) under reflux in tetrahydrofuran produced, in quantitative yields, the A-alkylidyne species [Mo2Cp(mu-SMe) (3){mu-(5-C5H4)(xylN)CN(xyl)C}] (4), in which a deprotonated Cp and both isonitrile ligands of 2b are now linked by new C-C and C-N bonds. Under prolonged reflux (72 h) in tetrahydrofuran 2b with either NaOH (suspension) or (Me4N) OH (in MeOH) in the presence of excess isonitrile RNC (R = xyl, Bu-t) was converted in high yields into the mixed (mu-alkylidyne)(mu-amino-oxycarbene) derivatives [Mo2Cp(mu-SMe)(2){mu-(eta(5)-C5H4)(xylN)CN(xyl)C}{mu-eta(1)(O),eta(1)(C)-OCNHR}] (R = xyl (5a1), R = Bu-t (5b2)) and [Mo2Cp(mu-SMe)(2){mu-(eta(C5H4)-C-5)(xylN)CN(xyl)C}{mu-eta(1)(O),eta(1)(C)-OCNMeR}] (R = xyl (6a)). All these products result from hydroxide-isonitrile coupling reactions. When the mixture of 2b, (Me4N) OH (excess), and ButNC (excess) in tetrahydrofuran was heated under reflux for a short time (2 h), complex 5b1 was formed in good yields. Compounds 5b1 and 5b2 are linkage isomers, which differ only in the mode of coordination of the mu-amino-oxycarbene ligand to the Mo1-Mo2 unit; 5b1 converts into 5b2 on prolonged heating. Reaction of the secondary amino-oxycarbene derivative 5a1 with a base (NaOH) and an alkylating agent R"4NBr (R" = Et, Bu-n) afforded the corresponding tertiary(amino)-oxycarbene complexes [Mo2Cp(mu-SMe)(2){mu-(eta(5)-C5H4)(xylN)CN(xyl)C}{mu-eta(1)(O),eta(1)(C)-OCNxylR"}] [R" = Et (6b), Bu-n (6c)]. On heating a tetrahydrofuran solution of the mu-alkylidyne compound 4 with NaOH (suspension) and an excess of either xylNC or (BuNC)-N-t, the mixed mu-alkylidyne and mu-amino-oxycarbene species 5a1 and 5b2 were obtained, demonstrating that 4 is an intermediate in the formation of 5a1 and 5b2 from 2b. Treatment of the mixed isonitrile-nitrile species [Mo2Cp2(mu-SMe)(3)(MeCN)(xylNC)](BF4) (3), containing a labile MeCN group, under reflux in tetrahydrofuran with NaOH (suspension) afforded quantitatively the mu-aminooxycarbene compound [Mo2Cp2(mu-SMe)(3){mu-eta(1)(O),eta(1)(C)-OCNHxyl}] (7). All new complexes have been characterized by elemental analyses and spectroscopic methods, supplemented for 5a1, 5b1, 5b2, 6a, 6b, and 7 by X-ray diffraction studies.