Investigations into the reactivity of an anionic gallium (I) N-heterocyclic carbene analogue

• Main Author: Mills, David P.
• Published: Cardiff University 2007
• Subjects: 547.05
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.584075

This thesis is mainly concerned with investigations into the reactivity of the gallium(I)-heterocyclic carbene (NHC) analogue, K(tmeda) :Ga{ N(Ar)C(H) 2} (Ar = C6H3Pr'2-2,6). Reactions of germanium, tin and lead alkyls, aryls, halides and heterocycles with K(tmeda) :Ga{ N(Ar)C(H) 2} afforded complexes such as K(tmeda) Sn{CH(SiMe3)2}2{Ga{ N(Ar)C(H) 2}}, which exhibits the first structurally characterised Ga Sn bond in a molecular complex. Group 6, 9 and 11 metal halide complexes were treated with K(tmeda) :Ga{ N(Ar)C(H) 2}, yielding complexes such as (IPr)Cu{Ga{ N(Ar)C(H) 2}} and (IPr)Ag{Ga{ N(Ar)C(H) 2}}. These complexes exhibit the first structurally characterised Ga Cu and Ga Ag bonds in molecular complexes. A study of the reactivity of (lPr)Cu{Ga{ N(Ar)C(H) 2}} with unsaturated organic substrates suggested that the Ga Cu bond is quite inert. Salt metathesis reactions of group 10 metal halide complexes with K(tmeda) :Ga{ N(Ar)C(H) 2} afforded complexes such as (dppe)Pt{Ga{ N(Ar)C(H) 2} }2. An investigation into the further reactivity of this complex towards ter/-butylphosphaalkyne yielded a platinum(II) complex, (dppe)Pt{Ga{ N(Ar)C(H) 2}}{Ga{ PC(Bul)C(H)- (NAr)C(H)N(Ar) }}, which exhibits a formally anionic P,N-heterocyclic gallium(I) ligand. The kinetics of the formation of this complex were studied. A novel gallium(III) complex, GaI2{C(But)P(H)C(But)=P} 2, was formed by the disproportionation reaction of :Sn(n4-P2C2But2) with "Gal". The oxidative insertion reaction of K(tmeda) :Ga{ N(Ar)C(H) 2} with FisoH yielded the gallium(III) hydride, {N(Ar)C(H)N(Ar)-K}(H)Ga{ N(Ar)C(H) 2}. Reaction of the digallane(4), Ga{ N(Ar)C(H) 2} 2, with N3-SiMe3 afforded the paramagnetic complex, {u- N(SiMe3)}Ga{ N(Ar)C(H) 2'} 2, which was studied by EPR spectroscopy. A synthetic route to the novel gallium(I) NHC analogue, K(tmeda) :Ga{ N(Ar)C(Me) 2}, is also described. Work performed in Monash University, involving bulky amidinate and guanidinate ligands, is also discussed. A novel cationic boron heterocycle, BrB(Giso) + (Giso" = {N(Ar)}2CNCy2 l, was synthesised from BBr3 and the gallium(I) guanidinate, :Ga(Giso). The use of Sm(Giso)2 as a one-electron reducing agent is exploited in the coupling of two molecules of CS2 by formation of a C S bond to yield {Sm(Giso)2}2(uvr 2:Ti2-SCSCS2). The synthesis of novel rj6-arene rhodium(I) complexes such as (rj4-COD)Rh(r 6-Giso), and their thermal conversion into thermodynamically more stable r 2-chelating forms, are also reported.