The odd nature of main group organometallic polyynes complexes

Abstract

This thesis describes the study of tungsten complexes bearing a range of odd number polyyne ligands, with a strong emphasis on the installation of a terminally capping main-group substituent. The development of these complexes utilised a diverse range of synthetic methods, with further reactivity studies performed highlighting the synthetic versatility of these molecules.

The bromocarbyne complex [W(CBr)(CO)2(Tp*)] (Tp* = HB(C5H8N2)3) a C1 ligand scaffold, can undergo mild cross-coupling with terminal alkynes (HCCR) under typical Sonogashira reaction conditions to provide a range of C3 propargylidyne complexes [W(CCCR)(CO)2(Tp*)] (R = tBu, Ph, C6H4NH2, C6H4NO2, Fc, CPh3, SiPh3, GePh3, BC5H7O4N). Alternative palladium mediated reactions such as the Stille cross-coupling reaction was utilised to generate bimetallic species [W2(-CCCC)(CO)4(Tp*)2] and the diphenylsilylinterrupted complex [W2(-CCCSi(Ph2)CCC)(CO)4(Tp*)2] which can be further reacted with two equivalence of AuCl(THT) (THT = SC4H8) resulting in the isolation of the tetrametallic complex [W2(-AuCl)2(-CCCSiPh2CCC)(CO)4(Tp*)2] where the AuCl fragment has added across the tungsten-carbon triple bond.

Attempting to extend the cross-coupling protocols to group 15 (pnicto)propargylidyne were unsuccessful, hence functionalisation of the trimethylsilylpropargylidyne [W(CCCSiMe3)(CO)2(Tp*)] a C3 scaffold was employed. Treatment of [W(CCCSiMe3)(CO)2(Tp*)] with MeLi lead to nucleophilic attack of the Cgamma generating the anionic allenylidene complex [W(=C=C=CMe(SiMe3))(CO)2(Tp*)]- in situ. Subsequent treatment with electrophiles (H2O, MeI) results in electrophilic attack at the Cbeta providing the vinylcarbyne complexes [W(CC(R)CSiMe3)(CO)2(Tp*)] (R = H, Me) as a mixture of E- and Z-isomers. Reaction with Br2 gives the bisvinylcarbyne species Z,Z-[W2(-CC(=C{SiMe3}Me)C(=C{SiMe3}Me)C)(CO)4(Tp*)2] where oxidative coupling has occurred at the Cbeta. En route to group 15 propargylidyne complexes, [W(CCCSiMe3)(CO)2(Tp*)] was treated with silver nitrate acquiring a green solid containing a mild nucleophilic source of [WAg(-CCC)(CO)2(Tp*)] that can be further reacted with PPh2Cl and AsPh2Br resulting in the isolation of pnictopropargylidynes [W(CCCPnPh2)(CO)2(Tp*)] (Pn = As, P).

Reactivity studies conducted on the diphenylphosphinopropargylidyne complex [W(CCCPPh2)(CO)2(Tp*)] with chalcogen transfer reagents oxidise at the phosphorus centre to give PV complexes [W(CCCP(=Ch)Ph2)(CO)2(Tp*)] (Ch = O, S, Se). Treatment with BH3SMe2 provides the Lewis adduct complex [W(CCCPPh2BH3)(CO)2(Tp*)]. In similar fashion both pnictopropargylidynes can coordinate to coordinatively unsaturated metal centres resulting in the isolation of -CCCP bridged bimetallic complexes [WM(-CCCPnPh2)(CO)2(Tp*)(Cl)2(Lfac)] (M(Lfac) = Ru(C6H3Me3), Rh(C5Me5)). The reaction with AuCl(THT) unexpectedly resulted in the isolation of multimetallic complexes [W2(-CC(PPh2AuCl)=C(PPh2AuCl)CCC)(CO)4(Tp*)2] and [W2(AuCl)(-CC(Au)C(AsPh2)CCC)(CO)4(Tp*)2]2 that contain both vinylcarbyne and propargylidyne motifs. Attempting to coordinate two equivalents of the diphenylphosphinepropargylidyne complex on to a single rhenium centre by ligand substitution with [Rh(CO)3(THF)2Br] leads to a Bergman-type cyclisation reaction where a diradical is formed that reacts with oxygen to provide furan [W2Re{-C(C4O(PPh2)2)C})(CO)7(Tp*)2(Br)] and [W2Re{-C(C5O2(PPh2)2)}(CO)7(Tp*)2(Br)] pyran complexes. Additionally the typical bimetallic complex [WRe(-CCCPnPh2)(CO)5(Tp*)(Br)] as a side product.

Applying the Sonogashira cross-coupling reaction between [W(CBr)(CO)2(Tp*)] and trimethylsilylbutadiyne (HCCCCSiMe3) results in the isolation in the first trimethylsilylpentagylidiyne complex [W(CCCCCSiMe3)(CO)2(Tp*)] a C5 scaffold where subsequent reactivity was explored. Show more