Structure and Bonding in Hartwig Stretched η³-Hydridoborate σ-Complex of Niobium(III)

Abstract

Ab initio calculations at the SCF, MP2, CASSCF, and CASPT2 levels of theory with basis sets using atomic pseudopotentials have been carried out for the stretched eta(3)-hydridoborate sigma-complex of niobium, [Cl2Nb(H2B(OH)2)], in order to investigate the nature and energetics of the interaction between the transition metal and the eta(3)-hydridoborate ligand. The geometry of the complex [Cl2Nb(H2B(OH)2] and its fragments [Cl2Nb](+) and [H2B(OH)2](-) were optimized at SCF and CASSCF levels. These results are consistent with [Cl2Nb(eta(3)-H2B(OH)2)] being a Nb(III) complex in which both hydrogen and boron of the [eta(3)-H2B(OH)2](-) ligand have a bonding interaction with the niobium preserving stretching B-H bond character. The calculated values of DEF (energy required to restore the fragment from the equilibrium structure to the structure it takes in the complex) for [Cl2Nb](+) are 5.35 kcal/mol at SCF, 3.27 kcal/mol at MP2, 4.80 kcal/mol at CASSCF, and 2.82 kcal/mol at CASPT2 and for [H2B(OH)2](-) 21.13 kcal/mol at SCF, 23.85 kcal/mol at MP2, 20.69 kcal/mol at CASSCF, and 23.48 kcal/mol at CASPT2. Values of INT (stabilization energy resulting from the coordination of distorted ligand to the metal fragment) for the complex [Cl2Nb(H2B(OH)2)] are -239.35 kcal/mol at SCF, -260.00 kcal/mol at MP2, -230.76 kcal/mol at CASSCF, and -252.60 kcal/mol at CASPT2. For the complex [(eta(5)-C5H5)2Nb(H2B(OH)2)], calculations at the SCF and MP2 levels were carried out. Values of INT for [(eta(5)-C5H5)2Nb(H2B(OH)2)] are -169.93 kcal/mol at SCF and -210.62 kcal/mol at MP2. The results indicate that the bonding of the [eta(3)-H2B(OH)2](-) ligand with niobium is substantially stable. The electronic structures of [Cl2Nb(H2B(OH)2)], [(eta(5)-C5H5)2Nb(H2B(OH)2)], and its fragments are analyzed in detail as measured by Mulliken charge distributions and orbital populations.

Coordination Modes of Boranes in Polyhydride Ruthenium Complexes: σ-Borane versus Dihydridoborate

“…The adopted coordination mode is thus the result of electronic effects. As expected for a dihydridoborate ligand,5a the Ru−B bond is significantly longer than in 2Bpin and 2Bcat , and its value of 2.346(4) Å is high enough to exclude a dihydride boryl coordination mode 6a. Moreover, the orientation of the BBN (the angle Cent(C1,C1‘)−B−Ru is 177.9°) agrees with a dihydridoborate coordination.…”

“…The past decade has seen major conceptual advances in the field of borane activation . Landmark findings have been disclosed both in fundamental aspects of coordination chemistry and in catalysis. − Several reports have shown that boron-containing moieties can adopt several geometries when bound to both early- and late-transition-metal centers 6 that also support hydride ligands (see Figure ). Better knowledge has been gained on the properties of transition-metal boryl compounds,6a and isolation of a few σ-borane complexes has been achieved following the first report in 1996 by Hartwig et al − These two classes of compounds play a central role in key events in catalysis, such as B−H oxidative addition and reductive elimination steps.…”

Rhodium Boryl Complexes in the Catalytic, Terminal Functionalization of Alkanes

“…The strength of the B−H interactions in hydridoborate complexes depends on the substituents at boron. The B−H interaction in a hydridoborate structure with π-donating alkoxide groups on boron is much weaker than the B−H interaction in a hydridoborate structure lacking a π-donor group on boron. , In fact, the experimental and theoretical studies on the structure of complex 2 imply that there is a significant interaction of the dialkoxyboryl group with only one of the two hydride ligands. As a result of the weak B−H interaction involving a second hydride and a boryl group with alkoxo substituents, the barrier for isomerization of the complex with mutually trans methyl and dialkoxyboryl groups to a complex with mutually cis methyl and dialkoxyboryl groups is low.…”

Structure and coordinate bonding nature of the manganese–σ–borane complexes

“…Ab initio calculations have been performed for r-borane complexes [(g 5 -C 5 H 5 )Ti{H-B(OH) 2 } 2 ] and [(g 5 -C 5 H 5 )Ti{HB(H) 2 r-borate complexes [(g 5 -C 5 H 5 ) 2 Nb{H 2 B(OH) 2 }] [42], [(g 5 -C 5 H 5 )Nb{H 2 B(C 8 H 14 )] and [(g 5 -C 5 H 5 )Nb{H 2 B(H) 2 }] [43].…”