s‐ and p‐Block Dinuclear Metal(loid) Complexes Bearing 1,4‐Phenylene and 1,4‐Cyclohexylene Bridged Bis(amidinate) Ligands

Abstract

Treating two 2,6‐diisopropylphenyl (Dip) substituted, 1,4‐phenylene or 1,4‐cyclohexylene bridged, bis(amidine)s, viz. C6Hn{[Dip(H)N](DipN=)C}2‐1,4 (n = 4 (PhAmid2H2) or 10 (CyAmid2H2)), with groups 1 and 2 alkyl complexes, proceeded via alkane elimination and the formation of the lithium and magnesium bis(amidinate) complexes, [{(THF)2Li}2(µ‐PhAmid2)], [{(THF)3K(µ‐PhAmid2)K}∞], [(Et2O)IMg(µ‐PhAmid2)MgI(OEt2)2], and [{(Et2O)2IMg}2(µ‐CyAmid2)]. The crystal structures of the complexes reveal variable modes of coordination at the metal centre. Two lithium bis(amidinate) compounds have been utilized in salt elimination reactions with group 13 and 14 halides, yielding a series of bis(amidinato) aluminum(III), silicon(IV), germanium(II) and tin(II) halide complexes, viz. [(I2Al)2(µ‐PhAmid2)], [(X3Si)2(µ‐PhAmid2)] (X = Cl, Br or Cl/H), [(ClM)2(µ‐PhAmid2)] (M = Ge or Sn), and [(ClGe)2(µ‐CyAmid2)]. Attempts to reduce the bis(amidinato) metal(loid) halide complexes with a series of s‐block metal reducing agents have been carried out, with the aim of obtaining dinuclear or polymeric bis(amidinato) metal(I) systems. However, these reductions typically led to intractable mixtures of products. In other attempted reductions, treating [(Cl2HSi)2(µ‐PhAmid2)] with two N‐heterocyclic carbenes (NHCs), :C{(RNCMe)2} (R = Me (TMC) or Pri (IPrIMe)) led to single dehydrochlorination reactions, affording the cyclohexa‐2,5‐diene‐1,4‐diylidene bridged bis(diamide) silicon(IV) complexes, [{(NHC)Cl2Si}{µ‐(DipN)2C=(C6H4)=C(NDip)2}{SiHCl(NHC)}] (NHC = TMC or IPrIMe), in which the bis(amidinate) ligand has been transformed into a tetra(amide).

Reversible addition of tin(ii) amides to nitriles

“…The reaction of Sn[N(SiMe 3 ) 2 ] 2 with 1,4-dicyanobenzene in the 1 : 1 ratio led, even at −90 °C, to inseparable mixtures of the products of addition to one (heteroleptic amidotin(II) 4-cyanobenzamidinate (δ( 119 Sn) of 51) and both CuN groups (1,4phenylene bridged bis(amidotin(II) amidinate)) ( 5), comparable to already reported 1,4-phenylene bridged s-and p-block dinuclear metal(loid) complexes. 18 These products were identified spectroscopically ( 1 H and 119 Sn NMR) as virtual products of the lower steric barrier in comparison with the composition of products originating from the reactions of 1,2-and 1,3dicyanobenzenes. On the other hand, two molar equivalents of Lappert's stannylene react with 1,3-and 1,4-dicyanobenzenes (due to steric demands not with 1,2-dicyanobenzene even after 12 days) to heteroleptic 1,3-or 1,4-phenylene-bis(amidotin(II) amidinates) (4 and 5).…”

Synthesis, Characterization, and Reaction of Digermylenes

“…The reactivity of the representative digermylene 1,3-C 6 H 4 (OGeL) 2 (1) with sulfur and selenium was examined (Scheme 6). The oxidative additions proceeded straightforwardly to produce the products 1,3-C 6 H 4 [OGe(S)L] 2 (8) and 1,3-C 6 H 4 [OGe(Se)L] 2 (9), with the 1 H NMR patterns similar to that of 1,3-C 6 H 4 (OGeL) 2 (1).…”

“…1 H NMR (400 MHz, C 6 D 6 , 298 K, ppm): δ = 7.12 (m, 12H, Ar-H), 6.91 (m, 2H, Ph-H), 6.74 (m, 1H, Ph-H), 6.52 (s, 1H, Ph-H), 4.87 (s, 2H, γ-CH), 3.45-3.53 (m, 4H, CHMe 2 ), 1.55 (s, 12H, CMe), 1.51 (br, 12H, CHMe 2 ), 1.15-1.18 (dd, J = 6.7 Hz, 24H, CHMe 2 ), 1.08 (d, J = 6.8 Hz, 12H, CHMe 2 ). 13 (9). A solution of 1,3-C 6 H 4 (OGeL) 2 (0.545 g, 0.5 mmol) and selenium (0.078 g, 1 mmol) in toluene (40 mL) was stirred at 85 °C for 12 hours.…”

“…One representative example is the digermylene oxide with the oxygen atom connecting the two Ge(II) centers [5] . Greater spacing distances between two Ge(II) sites have been achieved by using p ‐benzenenediamido, [6] p ‐phenylene, p ‐biphenylene, [7] p ‐terphenylene, [8] cyclohexylene, [9] or flexible alkyl chains [10] linkers in specially designed ligands. Intriguingly, the elimination of HCl from the β ‐diketiminate ligand supported germylene chloride LGeCl (L=CH[C(Me)NAr] 2 , Ar=2,6‐ i Pr 2 C 6 H 3 ) [11] gave a heterofulvene‐like germylene L′Ge (L′=HC[(C−CH 2 )CMe](NAr) 2 ) (Scheme 1), [12] which unexpectedly produced digermylenes by reactions with dibromoethane, [12] HN(SiMe 3 ) 2 , [13] PhC(N t Bu) 2 GeCl, [14] or (HO) 2 BPh [15] .…”

Calcium and Magnesium Bis(β-diketiminate) Complexes: Impact of the Alkylene Bridge on Schlenk-Type Rearrangements

“…Although dinuclear bis­(amidinate), bis­(amidoamine), bis­(β-diketiminate), bis­(guanidinate), bis­(iminopyrrolide), and bis­(salicylaldiminate) , complexes of the alkaline-earth metals have been reported in the past, the number of examples is significantly smaller compared to those including p-block elements or transition metals . One reason for the lower numbers is the intrinsic reactivity of alkaline-earth-metal complexes, which are affected by the Schlenk equilibrium in solution.…”