Synthesis, crystal structures and reactions of sila- and germa-beta-diketiminates

Addition of ArCN or PhCN to LiSiR3(thf)n(n= 0 or 3) or LiGeR3(thf)3 gave the lithium 3-sila- or 3-germa-beta-diketiminates [Li{(N(R)C(Ar))2SiR}D]1 or [Li{(N(R)C(Ph))2GeR}]22, respectively [Ar = 2,6-Me2C6H3; R = SiMe3; D =(thf)2(1a), NCAr (1b), or (NCAr)2(1c)]. Compound 1a with an equivalent portion of the heavier alkali metal tert-butoxide gave the appropriate dinuclear metal complex [M{(N(R)C(Ar))2SiR}]D]2[M = Na, D absent (3), or M = Rb, D = NCAr (5)] or [K{mu-(N(R)C(Ar))2SiR}]24; while 1a with Hg2Cl2 gave Hg[SiR{C(Ar)=NR}2]26. Thus, the ligand is (i) N,N-chelating in the mononuclear lithium complexes 1a–1c, (ii)Si-terminally bonding in the Hg(II) complex 6, (iii) not only N,N-chelating but also Si- (3, 5) or Ge- (2) bridging in the Na, Rb or Li dinuclear complexes, and (iv)N,N,Si-bridging in the K complex 4. Treatment of the lithium 3-sila-beta-diketiminate 1a with H–C5H5, Cl–TiCp2Cl, Br–CH2CH2Br or Br–HgBr, Me3Si–Cl, or Me3Sn–Cl yielded the appropriate silane Si(R)X[C (Ar)=NR]2(X = H 7, Cl 8, Br 9, SiMe310 or SnMe311); whereas with two equivalents of methanol the product was Si(R)OMe[C(Ar)=NR][C(H) (Ar)–N(H)R]12. The reaction between 2 and half an equivalent of NiCl2 or PdCl2 afforded the digermane [Ge(R){C(Ph)NR}2]213. The X-ray structures of the crystalline compounds 1b, 5, 6, 8, 9, 11 and 13 are reported; those for 1c, 2, 3 and 4 were described in preliminary publications. For the four latter, as well as 5, it is evident that the alkali metal 3-sila- or 3-germadiketiminates are zwitterionic (unlike the 3carba-z-delocalised analogues) having significant negative charge localised at the 3-Si or 3-Ge atom and localised CN double and E–N (E = Si or Ge) single bonds. Reaction pathways and solution NMR data are discussed.