Abstract
A novel trivalent diniobium(III) complex supported by three bulky pyridyl diamido ligands Me[N2N]2- (Me[N2N] = 2,6-bis(trimethylsilylamido)pyridine) is prepared. The reaction between NbCl3(DME) (DME = H3COCH2CH2OCH3) and Li2Me[N2N] yields the title compound Nb2(mu-Me[N2N])3 (1). Reaction of 1 with SnCl2 produecs (ClNb)(mu-Me[N2N])3(Nb) (2). Treatment of 1 with TMSN3 (TMS = Me3Si), a major product, symmetric bisimido complex (TMSNNb)2(mu-Me[N2N])3 (4), and a minor product, asymmetric azido imido complex (TMSNNb)(mu-Me[N2N])2(mu-Me[NNN])(NbN3) (5) are obtained. A symmetric bis(mesityl azido) complex (MesN3Nb)2(mu-Me[N2N])3 (3) (Mes = 2,4,6-Me3C6H2) is obtained when 1 is treated with MesN3. Upon treatment of 1 with S, Se and Te gives rise to the formations of niobium(V) chalcogenide (ENb)2(mu-Me[N2N])3 (E = S, 7; Se, 8; Te,10) and (SeNb)(mu-Me[N2N])2(mu-Me[NNN])(Nb) (9) as respective major and minor products, concomitant with the rupture of the Nb＝Nb double bond. Moreover, 1 can also be doubly oxygenated via an oxygen atom transfer from pyridine N-oxide to produce (ONb)2(mu-Me[N2N])3 (6). The Nb＝Nb double bond of 1 can also be split upon addition of organic azides. Treatment of VCl2(THF)4 with Li2t-BuPh2[N2N] (t-BuPh2[N2N] = 2,6-bis(tert-butyldiphenylsilylamido)pyridine) gives [(THF)V](mu-t-BuPh2[N2N])2(Na) (11) or [(THF)2V]2(mu-t-BuPh2[N2N])(mu-Cl)2 (12), but, on the other hand, reaction of VCl2(TMEDA)2 (TMEDA = N,N,N',N'-tetramethylethylenediamine) with Li2i-Pr[N2N] (i-Pr[N2N] = 2,6-bis(triisopropylsilylamido)pyridine) gives rise to [(TMEDA)V]2(mu-i-Pr[N2N])(mu-Cl)2 (13). Interestingly, the reaction of CrCl2 with Li2Me[N2N] produces Cr4(mu-Me[N2N])3(Me[NNNH])(mu-Cl) (14), in which the core structure is a five-member ring. The addition of KC8 to 14 leads the isolation of Cr4(mu-Me[N2N])4 (15), in which the Cr metal core forms a four-member ring. The reaction of CrCl2 with more sterically hindered ligands Li2t-BuMe2[N2N] (t-BuMe2[N2N] = 2,6-bis(tert-butyldimethylsilylamido)pyridine), Li2t-Bu2Me[N2N] (t-Bu2Me[N2N] = 2,6-bis(di-tert-butylmethylsilylamido)pyridine), Li2i-Pr[N2N] produces [(THF)Cr]2(mu-t-BuMe2[N2N])2 (16), [(THF)Cr]2(mu- t-Bu2Me[N2N])2 (17), [(THF)Cr]2(mu-i-Pr[N2N])2 (18). Complexes 16, 17, 18 are similar in structures. Treament of Li2i-Pr[N2N] with CrCl3 produces [(THF)2LiCl2Cr]2(mu-i-Pr[N2N])(mu-Cl)2 (21). Furthermore, the reaction of 18 with KC8 in the presence of 18-crown-6 ether proudces a mixed-valence complex {Cr2(mu-i-Pr[N2N])2}[K(18-crown-6 ether)(THF)2] (19). Interestingly, treatment of 19 with Se gives a mixed-valence Cr25+ complex, {Cr2(mu-i-Pr[N2N])2(mu-Se)}[K(18-crown-6 ether)(THF)2] (20). Reaction of the bulkier ligand Li2dipp[N2N] and CrCl2 leads to the isolation of Cr(mu-dipp[N2N])2[Cr(Et2O)] (23). Treatment of 23 with KC8 and 18-crown-6 ether produces a mixed-valence Cr23+ complex {Cr2(mu-dipp[N2N])2}[K(18-crown-6 ether)(Et2O)] (24). Noteworthy is reduction of 23 with more than 3eq of KC8 produces a quintuply-bonded Cr22+ complexes {Cr2(mu-dipp[N2N])2}(K2) (25) with two K atoms embedded by phenyl rings and nitrogen atoms. Treatment of Li2R[N2N] with WCl3(DME) gives a series of tungsten complexes, W2(mu-Me[N2N])3 (26), (ClW)2(mu-t-BuMe2[N2N])2 (27), (ClW)2(mu-i-Pr[N2N])2 (28); all of them display W-W triple bonds. Furthermore, the reaction of MnCl2 and Li2t-BuPh2[N2N] leads to the isolation of Mn2(mu-t-BuPh2[N2N])2 (29). Treatment of 29 with PhCN produces [(PhCN)Mn]2(mu-t-BuPh2[N2N])2 (30). All complexes presented are fully characterized by multi-nuclear NMR spectroscopy and X-ray diffraction.