Michael J. Doyle

A unique lithium halide complex, [(LiBr)2·3HMPA·toluene]: synthesis from reaction of solid NH4Br with BunLi in HMPA (hexamethylphosphoramide)/toluene media, crystal structure showing two Li–Br units linked by three µ2-HMPA ligands, and detection of 7Li ⋯31P coupling in solutions of the complex

Reaction of solid NH4Br with BunLi and HMPA (hexamethylphosphoramide)(1 : 1 : 2 ratio) in toluene produces (LiBr)2·3HMPA·toluene, (1), shown by X-ray crystallography to contain (LiBr)2·3HMPA molecules whose two terminal Li–Br units are linked by three µ2-HMPA ligands and with toluene molecules lying between these units in the lattice; in arene solutions, the (LiBr)2·3HMPA units remain intact, giving rise in 7Li n.m.r. spectra to 1 : 3 : 3 : 1 quartets caused by through-bond (OP) coupling of each 7Li nucleus to three 31P(HMPA) centres.

Activation parameters for rotation about an M–Ccarb bond from temperature dependent 1H n.m.r. spectra of RhI carbene complexes

Restricted rotation on the n.m.r. time scale about the Rh–Ccarb bond in complexes [RhLEt(Y)Y′(Z)][LEt= [graphic omitted](Et)] is demonstrated; for trans-[Rh(LEt)2(CO)Cl], variable temperature observations provid rotational activation parameters including a relatively low activation energy (⩽ 10 kcal mol–1) and a negative activation entropy.

Successive complexation steps in the co-ordination kinetics of the dysprosium(III)-acetate system

By controlling the ratio of metal ion to ligand concentrations in the DyIII–acetate system, the complexation rate constant for the formation of the bisacetato-complex was found to be significantly larger than for the monoacetato-complex.

Diastereofacial selectivity in Diels–Alder reactions of a diene having a stereogenic centre carrying a silyl group adjacent to the diene system

The dienylmethylsilane (3) reacts with N-phenylmaleimide to give the adducts (4) and (5) in a ratio of 82 : 18, the major product having come from reaction with diastereoface selectivity in the sense (18). The same diene, however, reacts with dimethyl acetylenedicarboxylate in the opposite sense (19) to give only the adduct (25). These results are not only complementary to each other but are also complementary to the reactions of the dienes (6) and (22), having an oxygen substituent on the stereogenic centre in place of the silyl group, where the major reaction of (6) with N-phenylmaleimide is known to take place in the sense (20), and the major reaction of (22) with dimethyl acetylenedicarboxylate in the opposite sense (21).

Synthesis and crystal and solution structures of the 1 : 1 TMEDA complex of lithium thiocyanate, (LiSCN·TMEDA)n[TMEDA = Me2N(CH2)2NMe2]: a polymeric solid with Li+ ions linked by bifunctional linear SCN– ligands

The anhydrous complex (LiSCN·TMEDA)n(1)[TMEDA = Me2N(CH2)2NMe2] has been synthesised by a novel in situ route from solid NH4SCN and BunLi in TMEDA/hexane, and shown to have a polymeric chain crystal structure with Li–N[graphic omitted]CS ⋯ Li repeat units; in hydrocarbon solvents, however, (1) adopts a dimeric, purely N–Li bridged structure.

Substitution reactions of a heterodimetallic molybdenum–manganese complex

The reactions of [MoMn(µ-C5H4PPh2)(CO)7]1 with phosphines and with isonitriles have been studied. Less bulky phosphines give derivatives of 1 of the type [MoMn(µ-C5H4PPh2)(CO)6L], which are monosubstituted at the manganese atom [L = PPh2H 2a, PPh2Me 2b, PPhMe22c or P(OMe)32f] whereas more bulky phosphines substitute only at the molybdenum atom (L = PPh33a). Phosphines of intermediate bulk give both types of derivative depending on the reaction conditions (L = PPh2Et 2e or 3b, PPh2CHCH22d or 3c). Disubstituted derivatives, [MoMn(µ-C5H4PPh2)(CO)5L2][L = PPh2Me 4a, PPh2CHCH24b or P(OMe)34c], obtained by reaction of 1 with excess of the appropriate ligand, have one substituent on the manganese and one on the molybdenum atom. Isonitriles give derivatives [MoMn(µ-C5H4PPh2)(CO)6L](L = CNCH2Ph 2g or CNBut2h) which are monosubstituted at the manganese atom but in a different position to the phosphine derivatives 2a–2f. Thermolysis of the diphenylphosphine derivative 2a gives [MoMn(µ-C5H4PPh2)(µ-H)(µ-PPh2)(CO)5]5a and thermolysis of either one of the vinylphosphine derivatives 2d or 3c gives a complex [MoMn(µ-C5H4PPh2)(µ-PPh2CHCH2)(CO)5]6 in which the vinylphosphine ligand is bonded through phosphorus to manganese and through the vinyl group to the molybdenum atom. Hydrogenation of 6 gives 3b in a reaction which involves a transfer of the co-ordination of the vinylphosphine phosphorus atom from manganese to molybdenum. Addition reactions of 6 with CO and P(OMe)3 involve a similar transfer to give [MoMn(µ-C5H4PPh2)(CO)6(PPh2CHCH2)]3c and [MoMn(µ-C5H4PPh2)(CO)5(PPh2CHCH2){P(OMe)3}]7 respectively. The structures of [MoMn(µ-C5H4PPh2)(CO)6(PPh2Et)]3b and [MoMn(µ-C5H4PPh2)(µ-H)(µ-PPh2)(CO)5]5a have been determined by X-ray analysis.

Reaction of solid sodium hydride with solid ammonium thiocyanate in HMPA-toluene. An ESR spectroscopic investigation and crystal structures of the two products of the reaction, [(NaNCS•HMPA)2]∞ and (NaNCS•2HMPA)2

Abstract Reaction of solid NH4SCN with solid NaH and HMPA (1:1:2 molar ratios) in toluene produces two complexes, (NaNCS·HMPA)n (1), which has an S···Na-linked polymeric structure (n = 2∞) with a repeat dimeric unit of form SCN·Na(μ2-HMPA) 2Na·NCS, and (NaNCS·2HMPA)n (2), which is a discrete symmetrical dimer (n = 2) with two μ2-HMPA ligands and with terminal HMPA and NCS− ligands (one of each per Na centre) arranged trans; the reaction appears to proceed via an electrontransfer mechanism, radical species having been detected by ESR spectroscopy.

A metal-directed pyrazoline–1,5-diazapentadiene rearrangement of a novel [2 + 2] macrocycle: crystal and molecular structures of L3 and [Ni2(L2)]·5H2O

The condensation of pentane-2,4-dione with pyridine-2,6-dicarbohydrazide leads to a structurally characterised [2 + 2] macrocyclic product containing two pyrazoline rings; reaction with transition metal ions leads to binuclear complexes of which the dinickel(II) complex has been structurally characterised and shown to contain two square-planar nickel ions co-ordinated to ring-opened pyrazoline groups.

Two monomeric, octahedral complexes of alkaline earth metal salts: syntheses, physical characteristics, and crystal structures of Srl2·4HMPA and Sr(NCS)2·4HMPA [HMPA = O : P(NMe2)3]

The complexes (Srl2·4HMPA)n, (1), and [Sr(NCS)2·4HMPA]n, (2), [HMPA = O : P(NMe2)3], were synthesised by reactions of Sr metal, NH4X solids (X = I and SCN, respectively), and HMPA (1:2:4 molar amounts) in toluene, and several HMPA complexes of calcium and barium halide and thiocyanate salts have been made by analogous routes; X-ray diffraction has shown that both Sr species have discrete molecular (n=1), octahedral structures, the X groups being trans in (1) but cis in (2).

Evidence for a radical-forming process during the reaction of solid NH4SCN with n-butyl-lithium and hexamethylphosphosphoramide (HMPA) in toluene: crystal structure of the product, (LiNCS·2HMPA)2

The complex (LiSCN·2HMPA)n, (1)[HMPA = O:P(NMe2)3], was synthesised by the reaction of solid NH4SCN with BunLi and HMPA (1 : 1 : 2 molar ratios) in toluene and shown to have an asymmetrical dimeric structure (n= 2) comprising terminal (HMPA)2Li– and (SCN)2Li– units whose metal centres are then bridged by two µ2-HMPA ligands; e.s.r. spectroscopic investigations on the reactions system (which proceeds through a series of colours) have detected the intermediacy of thiocyanate-based radical species.