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N-Heterocyclic carbenes and their heavier homologues are, in part, stabilized by delocalization of the N lone pairs into the vacant p-orbital at carbon (or a heavier Group 14 element center). These interactions are usually absent in the corresponding P-substituted species, owing to the large barrier to planarization of phosphorus. However, judicious selection of the substituents at phosphorus has enabled the synthesis of a diphosphagermylene, [(Dipp)2P]2 Ge, in which one of the P centers is planar (Dipp=2,6-diisopropylphenyl). The planar nature of this P center and the correspondingly short P-Ge distance suggest a significant degree of P-Ge multiple bond character that is due to delocalization of the phosphorus lone pair into the vacant p-orbital at germanium. DFT calculations support this proposition and NBO and AIM analyses are consistent with a Ge-P bond order greater than unity.

Reaction of the alkylzinc bromide Zn(C{SiMe3}2{SiMe2hpp})Br (hppH = 1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidine) with an excess of sodium hydride gives good yields of an unusual zinc hydride cluster, in which five zinc atoms are linked by (-H) bridges

The lithium reagent (3) reacts with a molar equivalent of anhydrous zinc bromide to give the dimeric compound (2a), in which zinc is four-coordinate. The product from a similar reaction with Li{C(SiMe3)2(SiMe2NPhMe)} is the lithium zincate [Li(THF)2(?-Br)2Zn{C(SiMe3)2(SiMe2NPhMe)}] (4), in which the zinc is only three-coordinate. The crystal structures of 2a and 4 have been determined.

The ‘lower order’ lithium cyanocuprates [Li(thf)2NCCu{C(SiMe3)3}]2 (1d), [Li(thf)2NCCu{C(SiMe3)2(SiMe2NMe2)}]2 (1e) and [Li(thf)NCCu{C(SiMe3)(SiMe2OMe)2}]2 (3) have been obtained from the reactions between copper(I) cyanide and the corresponding organolithium compounds. The compounds 1d and 1e have molecular structures containing four-membered Li2N2 rings but in 3 the lithium is coordinated by the methoxy groups of the ligand and almost linear LiNCCuC sequences are incorporated into fourteen-membered rings. Attempts to make ‘higher order’ cyanocuprates containing tri(organosilyl)methyl groups were unsuccessful and no reactions were observed when the cyanocuprate 1d was treated with alkyl halides or enones.

The organolithium compound Li(THF)(2){C(SiMe3)(2)(SiMe2NMe2)} reacted with one equivalent of MnCl2 to give [Mn(mu-Cl){C(SiMe3)(2)(SiMe2NMe2)}](2) (4) and with 0.5 equivalent of MnCl2 to give Mn{C(SiMe3)(2)(SiMe2NMe2)}(2) together with a small amount of the Mn-III compound [Mn(mu-O){C(SiMe3)(2)(SiMe2NMe2)}](2) (6) formed by adventitious admission of air. With CoBr2, the compound [Co(mu-Br){C(SiMe3)(2)(SiMe2NMe2)}](2) (7) was obtained. The reaction between the lithium compound Li(THF)(2){C(SiMe3)(2)(SiMe2OMe)} and MnCl2 in THF gave [Mn(THF)(mu-Cl){C(SiMe3)(2)(SiMe2OMe)}](2) (5). The crystal structures of compounds 4, 5, 6 and 7 were determined. Compounds 4 and 5 are the first manganese analogues of Grignard reagents containing Mn-C sigma-bonds to be characterised in the solid state. (C) 2002 Elsevier Science B.V. All rights reserved.

The complex [Li(TMEDA) {C(SiMe3)(2)SiMe(2)NMe2}] (1) (TMEDA = N,N,N,N-tetramethylethane-1,2,-diamine) was found to crystallise with an internally coordinated structure like that of [Li(THF)(2){C(SiMe3)(2)SiMe2Me2}] (THF = tetrahydrfuran). In contrast, the compound with Ph in place of NMe2 crystallised as a dialkyllithate [Li(TMEDA)(2)][Li{C(SiME3)(2)(SiMe2Ph)}(2)] (4). The reaction of 4 with MgBr2 gave the doubly bromide-bridged lithium-magnesium complex [Li(TMEDA)(mu -Br)(2)Mg{C(SiMe3)(2)(SiMe2Ph)} (THF)] (6), and that of [Li(THF){C(SiMe3)(2)(SiMe2C5H4N-2)}] gave the singly bridged compound [Li(THF)(3)(mu -Br)MgBr{C(SiMe3)(2)(SiMe2C5H4N-2)] (8). The Grignard reagents [Mg{C(SiMe3)(3)}I(OEt2)](2) (10) and [Mg{C(SiMe3)(2) (SiMe2Ph)} I(OEt2)](2) (11) were obtained from the reactions between (Me3Si)(3)CI and (Me2Ph)(Me3Si)CI, respectively, with magnesium metal and shown to have halide-bridged structures. The unsymmetrical dialkylmagnesium [MgBu{C(SiMe3)(2)(SiMe2NMe2)}(THF)] (13), was prepared from a mixture of LiBu, 1 and [MgBr2(OEt2)(2)]. (C) 2001 Elsevier Science B.V. All rights reserved.

The compounds HC(SiMe3)(SiMe2X)2, X = NMe2 or OMe, have been synthesized in several steps from the phenyl derivative HC(SiMe3)(SiMe2Ph)2 and metallated to give organometallic compounds of the type MC(SiMe3)(SiMe2X)2, M = K or Li. The structures of the compounds KC(SiMe3)2(SiMe2NMe2) and KC(SiMe2NMe2)3 consist of infinite chains in which cations are co-ordinated to both nitrogen and carbon centres, whereas the lithium compound [LiC(SiMe3)(SiMe2OMe)2]2 crystallises in a lattice of dimeric cage molecules. Structural trends in the series MC(SiMe3)n(SiMe2X)3-n, n = 0–3, M = K or Li, X = NMe2 or OMe, are discussed.