Organic intermetallic derivatives of tin and copperacetylide complexes

Abstract

Organic Intermetallic Derivatives of TinSome reactions of trialkyltin alkali metal derivatives were studied with the view to their use as synthetic reagents for the; introduction of the trialkyltin radical into other molecules and ultimately for syntheses of compounds in which tin would be covalently bonded to a metal from another chemical group.The reactions studied in ether-like solvents indicated that reaction between trialkyltin lithium compounds and organo-metallic halides led either to occurrence of metal-halogen exchange reactions or dissociation of the trialkyltin lithium. In the former case the symmetrical organo-dielement compounds were formed, e.g. hexamethylditin, cacodyl; and in the latter case, the alkyl lithium, produced by dissociation, reacted with the organo-metallic halide resulting in replacement of the halogen with an alkyl group. When, however, reaction between a trialkyltin lithium and an alkyl halide was carried out the expected reaction occurred, since, in this case, the reaction between the halide and any alkyl lithium produced by dissociation would be relatively slow, thus enhancing the chance of reaction between the alkyl halide and the trialkyltin group.Reactions carried out with elements from Group VI,sulphur and selenium, led to formation of the desired compounds methyltrimethyltin sulphide and methyltrimethyltin selenide. The latter compound contained a tin-selenium bond which does not appear to have been reported previously. In these reactions the trialkyltin radical was present in cationic form (as the bromide) and the Group VI elements in anionic form, so that metal-halogen exchange reactions would be most unlikely to occur.As the reactions with tin in cationic form had been successful a reaction between dimethylarsenic sodium and trimethyltin bromide was studied in liquid ammonia. However, results from this reaction again indicated that formation of the symmetrical di-element compounds occurred rather than combination of the trialkyltin radical with the dimethylarsenic group.As the reactions studied with trialkyltin alkali metal derivatives in ether-like solvents had shown that they behaved in a complex manner with a variety of reagents attention was directed to the rather limited use of liquid ammonia as a solvent for effecting reactions of the type discussed. In this solvent most organo-metallic halides are rapidly ammonolysed, tin and gallium however being exceptions, the reaction between trimethyltin sodium and dimethylgallium chloride mon-ammine was investigated. Therewas no indication that a tin-gallium bond was formed, tin being recovered as hexamethylditin and gallium as dimethylgallium amide.Part IICopperacetylide ComplexesSome new co-ordination complexes of copperacetylides and of silveracetylides, which appear hitherto unknown, were prepared and some of their properties investigated.In the series nitrogen, phosphorus, arsenic it was found that the order of stability of the coordination complexes was N ((P) As, those of phosphorus being by far the most stable. An important difference between the alkyl- and aryl- copperacetylide triethyl- phosphine complexes was observed in their behaviour in solution, in which the former dissociated(R-C≡CCuP(C2H5)3 R-C≡CCu + (C2H5)5P). Suchdissociation was also exhibited by the phenylsilver-acetylide-triethylarsine and -iso-propylamine complexes. The alkylcopperacetylide complexes oxidised rapidly in air, whereas the corresponding arylcopperacetylide compounds were much more stable. There was no indication that co-ordination of the metal acetylides occurred with sulphur co-ordinating reagents.Molecular weight determinations, where possible, showed that the co-ordination complexes were generally highly associated, the alkyls more so than the aryls, but the silver compounds less so than the corresponding copper co-ordination complexes. In the case of t-butylcopperacetylide, whichis soluble in organic solvents, molecular weight determinations confirmed earlier results, and showed that the copperacetylide was also highly associated.The relative stability of the copper- and silver acetylides and their co-ordination compounds has been discussed and attributed to co-ordination of the metal with an acetylene group from another molecule, in accordance with the conclusions of earlier work on t-butylcopperacetylide. .Any formation of a complex R-C≡C.ML (M=Gu or Ag, L = ligand) must be the result of successful competition between the M-acetylene co-ordination, which leads to the polymerization of R-C≡CM itself, and the co-ordination -M-L. Sincethe acetylides are, in general, only depolymerised by those ligands known to be the strongest donors to copper and silver (namely aliphatic tertiary phosphines), and since the resulting compounds R-C≡CM-L are themselves associated in solution, presumably by metal-acetylene group interaction, the last must be supposed to be very strong..