We make the case for benzo[c]quinolin-6-ylidene (1) as a strongly electron-donating carbene ligand. The facile synthesis of 6-trifluoromethanesulfonylbenzo[c]quinolizinium trifluoromethanesulfonate (2) gives straightforward access to a useful precursor for oxidative addition to low-valent metals, to yield the desired carbene complexes. This concept has been achieved in the case of [Mn(benzo[c]quinolin-6-ylidene)(CO)₅]⁺ (15) and [Pd(benzo[c]quinolin-6-ylidene)(PPh₃)₂(L)]²⁺ L=THF (21), OTf (22) or pyridine (23). Attempts to coordinate to nickel result in coupling products from two carbene precursor fragments. The CO IR-stretching-frequency data for the manganese compound suggests benzo[c]quinolin-6-ylidene is at least as strong a donor as any heteroatom-stabilised carbene ligand reported.

A series of new diphosphazane (PNP) ligands that contain 2,3,4,5-tetraethylphosphole or dibenzophosphole moieties has been synthesised. The new compounds have been screened for chromium-catalysed, selective ethene oligomerisation by in situ combination with CrCl₃(thf)₃ and methylaluminoxane (MAO). The ligands derived from 2,3,4,5-tetraethylphosphole produce highly active catalysts for ethene oligomerisation, which show excellent selectivity to C₆ and C₈ linear α-olefins. Complexes of the form [Cr(CO)₄L] were synthesised and studied by IR spectroscopy and single-crystal XRD. Variable-temperature NMR spectroscopy was used to investigate restricted PN rotation in compounds with bulky nitrogen substituents.

Highly active monomeric bis-cationic platinum(II) catalysts bearing small bite angle diphosphinamine [N,N-bis(diarylphosphino)amine] ‘PNP’ ligands efficiently catalyze Markovnikov hydration of terminal and internal alkynes to the corresponding ketones in water. Catalyst solubilization in water is achieved via ion pairing with anionic micelles formed by surfactant addition. The micelles ensure dissolution of apolar alkynes and promote the intimate contact between reagents and catalyst, while in organic-water media in the absence of surfactants the reaction is sluggish. Hydration products can be isolated by means of extraction with an apolar solvent and the catalyst, that remains confined in the aqueous phase, can be recycled up to four times without loss of catalytic activity.

Synthetic routes to cationic group 4 metallocene–(o-phosphanylaryl)oxido compounds of the type [Cp^R₂M(OPR₂)][WCA] (M = Ti, Zr, Hf; WCA = weakly coordinating anion) are described. The neutral mono-methyl complexes [Cp^R₂ZrMe(OPR₂)] 1–6 [Cp^R = Cp (1–3) or Cp* (4); OPR₂ = o-OC₆H₄(PtBu)₂ (1 and 4), OCMe₂CH₂(PtBu)₂ (2) or OC(CF₃)₂CH₂(PtBu)₂ (3)] are prepared by protonolysis of [Cp^R₂ZrMe₂] by the parent alcohol. The remaining methyl group in such complexes is best removed by protonolysis with [DTBP][B(C₆F₅)₄] (DTBP = 2,6-di-tert-butylpyridinium) to yield the desired cationic complexes 7 and 8 in the case of 1 and 4. In the case of 2 and 3, this method leads to side reactions. Treatment with B(C₆F₅)₃ yields the desired cations in all cases; however, side reactions with the generated [MeB(C₆F₅)₃] anion in subsequent reactions leads to problems. Hafnium analogues may be synthesised by similar routes. In the case of titanium, a different method must be adopted: chloride abstraction using [Et₃Si][B(C₆F₅)₄] from the parent complex [Cp₂TiCl(OPR₂)]. Such cationic group 4 metallocene–(o-phosphanylaryl)oxido compounds exhibit reactivity that is best described by the frustrated Lewis pair concept.