Neopentane-based tripodal CpL2 ligands: Synthesis and reactions of CH3C(CH2-eta(5)-C5H4)(CH2-eta(1)-PPh2)2RuCl; Hindered rotation of vinylidene ligands

The tripodal ligand [CH3C(CH2C5H4) (CH2PPh2)(2)](-) reacts with RuCl2(PPh3) (3) to produce CH3C(CH2-eta(5)-C5H4) (CH2-eta(1)-PPh2)(2)RuCl, [tripodCpL(2 )RuCl], 1. Complex 1 undergoes substitution of the chlorine function with v arious nucleophiles L' to produce [tripodCpL(2)RuL'](+). The carbonyl deriv ative (L' = CO) 2, isonitrile (L' = RNC) 3, nitrile compounds (L' = RCN) 4, and a tolane adduct (L' = eta(2)-PhC=CPh) 5 are obtained when 1 is treated with the appropriate Ligands in polar solvents. Halide accepters (e.g. TlP F6) are generally needed to promote these reactions. The cyanide derivative tripodCpL(2)RuCN (3a) is alkylated by F3CSO3CH3 to give the isonitrile der ivative [tripodCpL(2)RuCNMe](+) 3b. Terminal alkynes HC=CR produce vinylide ne compounds [tripodCpL(2)RuL'](+), where L' = C=CHR (R = tBu, 7b; R = Ph, 7c), or allenylidene derivatives, L' = C=C=CPh2 (6), depending on the natur e of R (R = CPh2OH for synthesis of 6). Trimethylsilylacetylene gives the p arent vinylidene species, L' = C=CH2 (7a), which is transformed to the Fisc her-type carbene compound, L' = C(OMe)Me (8), upon treatment with methanol. The vinylidene species 7 are deprotonated by NaOMe to produce the alkynyl compounds tripodCpL(2)RuC=CR (9). Methylation of 9 with F3CSO3CH3 results i n the vinylidene derivatives L' = C=C(Me)R (R - tBu, 7d; R = Ph, 7e), havin g two organic substituents at the terminal carbon centre. For all vinyliden e compounds with two different substituents at their terminal carbon atom, hindered rotation of the single-faced vinylidene pi-ligand about its Ru-C b ond is observed. Analysis by P-31- NMR spectroscopic coalescence measuremen ts as well as line-shape analyses reveals activation enthalpies of around 4 0 kJmol(-1) for this rotation, with small activation entropies of around +/ -10 Jmol(-1)K(-1). Solid-state structures of nine compounds of the type [tr ipodCpL(2)RuL'](+n) (n = 0, 1) demonstrate the remarkable conformational ri gidity of the tripodCpL(2)Ru template. They also show that the possible str ain imposed by linking the Cp Ligand and the two donor groups L in one and the same chelate scaffolding does not appear to impose a serious steric str ain on these templates.