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The 2-phosphinophosphinine 2-PPh-3-Me-6-SiMe-PCH (2) has been prepared and was shown to act as a κ-chelating ligand in cis-[RuCl(2)] (4). Complex 4 was a competent precatalyst for the room temperature transfer hydrogenation of acetophenone (0.1 mol% 4 and 0.5 mol% KOBu) and the conversion of methanol/ethanol mixtures to the advanced biofuel isobutanol in 50% yield and 96% selectivity.

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Desilylation of the 2-phosphinophosphinine 2-PPh 2-3-Me-6-SiMe 3-PC 5 H 2 with HCl gave 2-PPh 2-3-Me-PC 5 H 3 , demonstrating the late-stage modification of this bidentate heterocyclic ligand. Group 6 metal carbonyl complexes of these ligands showed κ 2-binding and very small bite-angles of 65.1-68.3°, and also demonstrated that the donor properties of 2phosphinophosphinines can be tuned readily by the presence of the SiMe 3 group which gives a more π-accepting phosphinine ligand. The properties of 2-phosphinophosphinines were compared to bidentate diphosphorus ligands computationally, contextualizing them in the Ligand Knowledge Base for bidentate P,P donor ligands (LKB-PP) and were found to occupy an area of ligand space adjacent to Ar 2 PN(R)NAr 2 ligands that have been successfully used in ethylene oligomerization reactions, but with well-separated properties in the second principal component. Testing 2-phosphinophosphinines in Cr-catalyzed ethylene oligomerization reactions showed key differences to standard PNP ligands in that a high proportion of alkyl-and alkenyl-cyclopentanes were formed. This demonstrates that the different donor properties of 2-phosphinophosphinines influence the reactivity of the key 7-membered metallacycle postulated in the metallacyclic reaction mechanism, generating products from isomerization and subsequent ethylene insertion. Alkyl-and alkenyl-cyclopentanes represent new products for the key industrial feedstock ethylene, with the alkenes having potential as new monomers, comonomers or additives for plastics. Computational evaluation of ligand properties and the resulting property maps can play a role in suggesting future ligand developments to change the selectivity of this industriallyrelevant system in the pursuit of new products generated from ethylene.

Two Rh complexes of the 2-phosphinophosphinine ligand 2-PPh2-3-Me-6-SiMe3-C5H2P (1) were prepared: dinuclear trans-[{Rh(CO)(Cl)(μ-1)}2] (2) and chelating [Rh(1)(COD)][B(ArF)4] (3). Despite the widespread use of Rh catalysts for the hydroboration of alkenes, 3 is reported to be the first Rh catalyst for ketone and ketimine hydroboration, with high activity observed at 0.1 mol% loading.