A Reactive Ru–Binaphtholate Building Block with Self-Tuning Hapticity

A versatile Ru–BINO building block is reported, which offers a straightforward entry point into the chemistry of atropisomeric binaphtholate complexes of ruthenium. Reaction of RuCl₂(PPh₃)₃ 6a with Tl₂((S)-BINO) affords Ru((S)-BINO)(PPh₃)₂ 7 as a mixture of isomers: in 7′, the BINO ligand is bound via η³-CCO,η¹-O′ donors, and in symmetrical 7″, via η³-CCO,η³-O′C′C′ interactions. The bis(enolate) BINO bonding mode in the latter, not previously observed for any metal, underscores the remarkable geometric and electronic flexibility of the binaphtholate moiety. The BINO ligand proves able to stabilize complexes containing as few as two, and as many as four, additional ligands in 7 and its derivatives, enabling a synthetic versatility that contrasts with that of the superficially similar o-catecholate complex Ru(o-cat)(PPh₃)₃. As with the important achiral Ru precursor 6a, complex 7 undergoes facile transformation into a range of products under mild conditions, including acetonitrile, pyridine, and vinylidene derivatives. Single-crystal X-ray structures are reported for three of these complexes: Ru(η³,η³-(S)-BINO)(PPh₃)₂ 7″, Ru(η³,η¹-(S)-BINO)(PPh₃)₂(MeCN) 9, and Ru(η³,η¹-(S)-BINO)(PPh₃)(py)₂ 11. ¹³C{¹H} NMR signatures are proposed for new and known BINO coordination modes (η¹-O,η¹-O′; η¹-C1,η¹-O′; η³-CCO,η³-O′C′C′; η³-CCO,η¹-O′; η⁶-C₆,η¹-O′), as a potential aid to further developments in late-metal BINO chemistry.