DINITROGEN, BUTADIENE AND RELATED COMPLEXES OF MOLYBDENUM - CRYSTAL-STRUCTURES OF [MO(N-2)(PME(3))(5)] AND [MO(ETA(3)-CH3CHCHCH2)(ETA(4)-C4H6)(PET(3))(2)][BF4]

The sodium amalgam reduction of [MoCl3(PEt(3))(3)] prepared in situ, under 2-3 atm of N-2, yielded the dimeric complex [{Mo(N-2)(2)(PEt(3))(3)}(2)(mu-N-2)] 1, which reacted with 3 and with 4 equivalents of PMe(3) to produce trans-[Mo(N-2)(2)(PMe(3))(3)(PEt(3))] 2 and trans-[Mo(N-2)(2)(PMe(3))(4)] 3, respectively. In the presence of an excess of PMe(3) (> 5 equivalents, under Ar) the known [Mo(N-2)(PMe(3))(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(N-2)(PMe(3))(3)(L-L)] (L-L = Me(2)PCH(2)PMe(2) 4b, Me(2)PCH(2)CH(2)PMe(2) 4c or Et(2)PCH(2)CH(2)PEt(2) 4d) and [Mo(N-2)(PMe(3)){N(CH(2)CH(2)PMe(2))(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(eta(4)C(4)H(6))(2)(PEt(3))(2)] 5a. Protonation of 5a, and of its PMe(2)Ph analogue 5b, produced the cationic but-2-enyls [Mo(eta(3)-CH3CHCHCH2)(eta(4)-C4H6)L(2)][BF4] (L = PEt(3) 6a or PMe(2)Ph 6b) in which the butenyl ligand exhibits the classical eta(3)-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 N-2 moiety with a Mo-N separation of 2.02(3) Angstrom. The Mo-C and Mo-H separations within the agostic unit of 6a are 2.48(2) and 1.9(2) Angstrom, respectively.