The application of a cobalt pincer complex, (PP Cl P)CoCl 2 , as a precatalyst for the hydroboration of terminal alkenes with pinacolborane (HBPin) is described. The reactions proceed rapidly under mild conditions (room temperature, 30 min) with low catalyst loadings (1 mol %) using KBEt 3 H (2.1 mol %) as an activator to afford terminal hydroboration products with very high selectivity for the anti-Markovnikov product. The precatalyst is effective toward vinyl arenes and aliphatic alkenes and proceeds to an 83−98% yield with these substrates. However, the functional group tolerance of the catalytic system is somewhat limited, as minimal conversion is observed with internal olefins or when pyridine, ketone, or allyl ether functional groups are present. Deuterium labeling studies and spectroscopic identification of the catalyst deactivation product suggest a (PPP)CoH active species.

The diphosphine, N-heterocyclic phosphenium (NHP + ) /phosphido (NHP -) containing ligand (PPP +/-) has been coordinated to rhodium to study the coordination chemistry of group 9 metals and NHP +/fragments. Addition of the chlorophosphine ligand PP Cl P to [Rh(COD)Cl]2 produces the complex (PP Cl P)RhCl ( 2), which can be reduced to form (PPP)RhPMePh2 (3), the asymmetric dimer [(PPP)Rh]2 (4) and the asymmetric dimer [(PPP)Rh(CN t Bu)]2 (5). Analysis of the solid-state structures and computational studies have provided insight into the electronic structure and bonding in 3-5, revealing that the NHP +/fragments in 3, 4 and 5 are best described using an NHP -/Rh I description. Both 3 and 5 were found to be reactive towards the S-H bond of thiophenol, generating (PPP)RhSPh ( 6) and (PPP)Rh(SPh)(CN t Bu) ( 7) respectively.

The bonding interactions and electronic structure of a diphosphine pincer ligand featuring an N-heterocyclic phosphenium/ phosphido (NHP ± ) central moiety with nickel are explored. Treating Ni(COD) 2 with the pincer ligand [PPP]Cl in the presence of a twoelectron phosphine donor ligand PMe 3 generates chlorophosphine complex (PP Cl P)Ni(PMe 3 ) (2a). The cationic Ni complex [(PPP)Ni-(PMe 3 )][BPh 4 ] (3a) can be prepared by subsequent halide abstraction from 2a with NaBPh 4 . The assignment of 3a as a Ni 0 /NHP + complex, based on analysis of structural parameters and computational investigations, lies in contrast to its previously reported group 10 M II / NHP − (M = Pd, Pt) analogues. The activation of O−H bonds across the Ni−P NHP bond is demonstrated by the addition of isopropanol to afford the metal hydride species [(PP OiPr P)Ni(PMe 3 )(H)][BPh 4 ] (4). Notably, the installation of a P−H bond in the NHP unit by treatment of 2a with LiAlH 4 yields (PP H P)Ni(PMe 3 ) (6). The ambiphilic nature of the P−H bond was demonstrated through reactivity studies of P−H bond cleavage in comparison to a Pd analogue (PP H P)Pd(PPh 3 ) (8).

The bonding interactions of a synthesized pincer-ligated manganese dicarbonyl complex featuring an N-heterocyclic phosphenium (NHP+) central moiety are explored. The pincer ligand [PPP]Cl was coordinated to a manganese center using Mn(CO)5Br and 254 nm light to afford the chlorophosphine complex (PPClP)Mn(CO)2Br (2) as a mixture of halide exchange products and stereoisomers. The target dicarbonyl species (PPP)Mn(CO)2 (3) was prepared by treatment of 2 with 2 equiv of the reductant KC8. Computational investigations and analysis of structural parameters were used to elucidate multiple bonding interactions between the Mn center and the PNHP atom in 3. The generation of a product of formal H2 addition, (PPHP)Mn(CO)2H (4), was achieved through the dehydrogenation of NH3BH3, affording a 2:1 mixture of 4syn :4anti stereoisomers. The nucleophilic nature of the Mn center and the electrophilic nature of the PNHP moiety were demonstrated through hydride addition and protonation of 3 to produce K(THF)2[(PPHP)Mn(CO)2] (6) and (PPClP)Mn(CO)2H (5), respectively. The observed reactivity suggests that 3 is best described as a Mn–I/NHP+ complex, in contrast to pincer-ligated dicarbonyl manganese analogues typically assigned as MnI species.