Key elements in this communication are a very efficient microwave synthesis of [RuCp(naphthalene)][PF(6)], the precursor of [RuCp(CH(3)CN)(3)][PF(6)], and a Pd-catalysed asymmetric hydrogenolysis to afford planar chiral ruthenium complexes with high levels of enantioselectivity using a bulky chiral phosphoramidite ligand.

Mono- and multinuclear complexes of ruthenium and [n]cycloparaphenylene (CPP, n = 5 and 6) were synthesized in excellent yields through ligand exchange of the cationic complex [(Cp)Ru(CH3CN)3](PF6) with CPP. In the multinuclear complexes, ruthenium selectively coordinated to alternate paraphenylene units to give bis- and tris-coordinated Ru complexes for [5] and [6]CPPs, respectively. Single-crystal X-ray analysis revealed the Ru was coordinated with η(6)-hapticity on the convex surface of CPP.

The efficient functionalization of planar chiral ruthenium naphthalene—and ruthenium indenyl—scaffolds is reported. Mild reaction conditions employing microwave heating have been developed for the derivatization of sensitive cationic naphthalene ruthenium complexes. In particular, a series of novel planar chiral monodentate phosphines and their gold(I) complexes have been synthesized and fully characterized by NMR spectroscopy and X-ray crystallography. Furthermore, the electronic properties of these phosphines (L) have been evaluated via the infrared CO stretching frequencies of the corresponding Ni(CO)3(L) complexes, providing valuable insight for the design and application of these chiral ligands in asymmetric catalysis

Access to highly enantioenriched planar chiral [Cr(5-bromonaphthalene)(CO)(3)] (6), [Ru(eta(5)-C(5)R(5))(5-bromonaphthalene)][PF(6)] (42) and [Ru(eta(5)-C(5)R(5))(4-bromoindene)] (44) was sought using asymmetric hydrogenolysis of [Cr(5,8-dibromonaphthalene)(CO)(3)] (5), [Ru(eta(5)-C(5)R(5))(5,8-dibromonaphthalene)] (39) and [Ru(eta(5)-C(5)R(5))(4,7-dibromoindene)] (40), respectively. Initial efforts focused on the chromium complex 5. Pd(0) catalysts with dimethoxyethane as the solvent and LiBH(4) or NaBH(3)CN as a hydride source worked best. Nineteen chiral bidentate phosphorus ligands were screened in this reaction. Asymmetric induction was low to modest with product ee's in the range of 4 to 52% and yields of 6 of up to 70%. Chiral phosphoramidite ligands proved superior and a bulky ligand derived from a Whitesell amine and 3,3'-diphenyl-binaphtol afforded 6 with an ee of 97%. The high enantioselectivity is largely due to the initial desymmetrization reaction though kinetic resolution also plays an important role as shown by the determination of a selectivity factor s=8.5 at -10 degrees C. Initially high ligand loadings (4 equiv/Pd) were necessary to achieve good asymmetric induction. This could be traced to the trapping of the chiral ligand by borane formed in the reaction. Addition of 1,4-diazabicyclo[2.2.2]octane (DABCO) suppressed this, and its addition led to the use of Pd and chiral ligand in a 1:1.2 ratio. Asymmetric hydrogenolysis of cationic dibromonaphthalene and neutral dibromoindenyl complexes of Ru cyclopentadienyl complexes was investigated and afforded the following results: [RuCp(5-bromonaphthalene)][PF(6)] (39a; 75%, 90% ee), [RuCp*(5-bromonaphthalene)] [PF(6)] (39b; 88%, 99% ee), [RuCp(4-bromoindenyl)] (44a; 72%, 96% ee), and [RuCp*(4-bromoindenyl)] (44b; 62%, 68% ee).

Access to planar chiral complexes has been sought by catalytic desymmetrisation of a prochiral complex via asymmetric Suzuki-Miyaura cross-coupling. High selectivities of up to 98% ee were achieved using a bulky chiral palladium catalyst.