Template Synthesis of NPN?Pincer-type Ligands at Titanium Usingan Ambiphilic Phosphide Scaffold

Ti-imido complex [TiCl(NtBu)(BIPP)] [1; BIPP =bis(iminophosphoranyl)phosphide ligand] reacts with terminalalkynes R-C???CH (R = phenyl, isopropenyl, cyclopropyl, and 2-pyridyl) via P-P bond cleavage of the BIPP ligand. The resultingcomplexes [TiCl(NPN ')(NPhPPh2)] (2a-d) contain a pincer-typeNPN ' phosphide ligand that incorporates the terminal alkyne andthe imido ligand from complex1. Complexes2a-dfeature twochiral centers (Ti and P) with interdependent absolute config-urations; thus, they are formed stereoselectively. Complex2a(R =phenyl) undergoes chloride abstraction with [Et3SiHSiEt3][B-(C6F5)4], yielding [Ti(NPN ')(NPhPPh2)][B(C6F5)4](3). Com-plex3is a moderately active and stereoselective initiator for thering-opening polymerization ofrac-lactide. Complex3activates theC???O bond of 4-iodobenzaldehyde to give complex4as a single diastereomer despite the presence of three chiral centers. Complex3undergoes transmetallation with SbCl3, yielding [Sb(NPN ')][B(C6F5)4](5) and [TiCl3(NPhPPh2)] (6) selectively. The bondingsituation in3and5was analyzed using Bader's atoms in molecules and the electron localization function, showing that the nitrogenatoms of the NPN ' ligand are electronically similar, and that the metal-phosphide interaction is more polar in the case of titanium.

Automated summary

A series of complexes with pincer-type ligands were synthesized via P-P bond cleavage reaction, which exhibited stereoselectivity and showed reactivity towards C???O bond activation and transmetallation.