Dinitrogen, butadiene and related complexes of molybdenum. Crystal structures of [Mo(N2)(PMe3)5] and [Mo(η3-CH3CHCHCH2)(η4-C4H6)(PEt3)2][BF4]
Abstract
The sodium amalgam reduction of [MoCl3(PEt3)3] prepared in situ, under 2–3 atm of N2, yielded the dimeric complex [{Mo(N2)2(PEt3)3}2(µ-N2)]1, which reacted with 3 and with 4 equivalents of PMe3 to produce trans-[Mo(N2)2(PMe3)3(PEt3)]2 and trans-[Mo(N2)2(PMe3)4]3, respectively. In the presence of an excess of PMe3(>5 equivalents, under Ar) the known [Mo(N2)(PMe3)5]4a was the final product. This synthetic methodology allowed the preparation, for the first time, of the pure trans-bis(dinitrogen) compound 3. Complexes of the type [Mo(N2)(PMe3)3(L–L)](L–L = Me2PCH2PMe24b, Me2PCH2CH2PMe24c or Et2PCH2CH2PEt24d) and [Mo(N2)(PMe3){N(CH2CH2PMe2)3}]4e were also synthesized and structurally characterized by spectroscopic methods. Upon reaction with C2H4, under mild conditions, 1 gave the bis(butadiene) derivative [Mo(η4C4H6)2(PEt3)2]5a. Protonation of 5a, and of its PMe2Ph analogue 5b, produced the cationic but-2-enyls [[graphic omitted]CHCHCH2)(η4-C4H6)L2][BF4](L = PEt36a or PMe2Ph 6b) in which the butenyl ligand exhibits the classical η3-allylic co-ordination in addition to an agostic Me–Mo interaction. Compounds 4a and 6a were structurally characterized by X-ray crystallography. The Mo atom of 4a resides on a crystallographic mirror plane and is bound to the N2 moiety with a Mo–N separation of 2.02(3)Å. The Mo–C and Mo–H separations within the agostic unit of 6a are 2.48(2) and 1.9(2)Å, respectively.