The organometallic chemistry of conjugated, low-coordinate phosphacarbon compounds

• Main Author: Trathen, Nicola
• Published: University of Sussex 2015
• Subjects: 540; QD0241 Organic chemistry
• Online Access: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.647929

Organometallic complexes incorporating low-coordinate phosphorus have been synthesised with a view to better understanding the physical and electronic properties and reactivity of such compounds, along with synthetic methodologies to furnish them. Novel ruthenium complexes of the type [Ru(CO){κ3-N,C,P-P(PzR′R″)CH(R)}(PPh3)2] (Pz = pyrazolyl) have been synthesised via addition of pyrazolates to complexes of the type RuCl(CO)(PPh3)2(P=CHR). The general structure of the resultant products was elucidated, with a Ru–C–P three-membered ring and bridging pyrazolyl unit confirmed by heteronuclear NMR spectroscopy and X-ray diffraction studies. The nature of the R groups was found to affect the nature of the P–C bond, which lies between a typical single and double P–C bond. The formation of these complexes demonstrated for the first time the ambiphilic nature of the parent ruthenaphosphaalkenyl systems, which was explored by both DFT calculations and their reactivity upon addition of various nucleophiles and electrophiles. A range of extended π-systems have been sought for their potential utility in the synthesis of phosphapolyynyl fragments. Complexes of the type [Tp′M(CO)2(≡CC≡CR)] were pursued, (where R = CO2R') via a variety of synthetic protocols including traditional Sonogashira methodologies, in situ formation of the propargylidyne moiety (M≡C≡C–) and cross-coupling reactions between a terminal alkyne and Au(PPh3)-terminated propargylidynes. Additionally, a range of metal–alkynyl complexes were pursued via vinylidene/alkyne tautomerism reactions. In particular, the successful synthesis of a range of complexes of the type [RuCl(dppe)2(=CH=CR)][OTf] and [RuCl(dppe)2(C≡CR)] is discussed with characterization of the novel compounds by IR and heteronuclear NMR spectroscopies, mass spectrometry and X-ray diffraction studies. Finally, synthesis of a novel series of cyaphide-containing compounds is demonstrated. The physical and chemical properties of this elusive ligand are discussed and the electronic properties studied computationally. Attempts were also made to furnish complexes with η1-coordination of the phosphorus lone pair to a second metal centre, i.e. complexes of the type [(dppe)2(RC≡C)Ru–C≡P–MLn].