title: Probing mesitylborane and mesitylborate ligation within the coordination sphere of Cp*Ru(P(i)Pr3)+: a combined synthetic, X-ray crystallographic, and computational study.
abstract: The reaction of Cp*Ru(P(i)Pr(3))Cl (1) with MesBH(2) (Mes = 2,4,6-trimethylphenyl) afforded the mesitylborate complex Cp*Ru(P(i)Pr(3))(BH(2)MesCl) (2, 66%). Exposure of 2 to the chloride abstracting agent LiB(C(6)F(5))(4)·2.5OEt(2) provided [Cp*Ru(P(i)Pr(3))(BH(2)Mes)](+)B(C(6)F(5))(4)(-) (3, 54%), which features an unusual η(2)-B-H monoborane ligand. The related borate complex Cp*Ru(P(i)Pr(3))(BH(3)Mes) (5, 65%) was prepared from 1 and LiH(3)BMes. Attempts to effect the insertion of unsaturated organic substrates into the B-H bonds of 3 were unsuccessful, and efforts to dehydrohalogenate 2 using KO(t)Bu instead afforded the mesitylborate complex Cp*(P(i)Pr(3))Ru(BH(2)MesOH) (6, 48%). Treatment of 1 with benzyl potassium generated an intermediate hydridoruthenium complex (7) resulting from dehydrogenation of a P(i)Pr fragment, which in turn was observed to react with MesBH(2) to afford the mesitylborate complex Cp*(P((i)Pr)(2)(CH(3)CCH(2)))Ru(BH(3)Mes) (8, 47%). Crystallographic characterization data are provided for 2, 3, 5, 6, and 8. A combined X-ray crystallographic and density functional theory (DFT) investigation of 3 and 5, using Natural Bond Orbital (NBO) and Atoms in Molecules (AIM) analysis, revealed that 3 and 5 are best described as donor-acceptor complexes between a Cp*(P(i)Pr(3))Ru(+) fragment and a bis(η(2)-B-H) coordinating mesitylborane(borate) ligand. Significant σ-donation from the B-H bonds into the Ru(II) center exists as evidenced by the NBO populations, bond orders, and AIM delocalization indices. In the case of 3, the vacant p orbital on boron is stabilized by Ru→B π back-donation as well as by resonance with the mesityl group.
authors.affiliation: Department of Chemistry, Dalhousie University, Halifax, Nova Scotia B3H 4J3, Canada.
authors.forename: Kevin D
authors.initials: KD
authors.lastname: Hesp
authors.forename: Felix O
authors.initials: FO
authors.lastname: Kannemann
authors.forename: Matthew A
authors.initials: MA
authors.lastname: Rankin
authors.forename: Robert
authors.initials: R
authors.lastname: McDonald
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Ferguson
authors.forename: Mark
authors.initials: M
authors.lastname: Stradiotto
mesh_terms: D001880:Boranes / Q000737:chemistry*; D001881:Borates / Q000737:chemistry*; D018360:Crystallography, X-Ray; D008958:Models, Molecular; D008968:Molecular Conformation; D009942:Organometallic Compounds / Q000138:chemical synthesis* / Q000737:chemistry*; D011789:Quantum Theory; D012428:Ruthenium / Q000737:chemistry*
chemical_list: D001880:Boranes; D001881:Borates; D009942:Organometallic Compounds; D012428:Ruthenium