Coordination modes of boranes in polyhydride ruthenium complexes:: σ-Borane versus dihydridoborate

被引:87
作者
Lachaize, S
Essalah, W
Montiel-Palma, V
Vendier, L
Chaudret, B
Barthelat, JC
Sabo-Etienne, S
机构
[1] CNRS, Lab Chim Coordinat, F-31077 Toulouse, France
[2] Univ Toulouse 3, UMR 5626, IRSAMC, Lab Phys Quant, F-31062 Toulouse, France
关键词
D O I
10.1021/om050276l
中图分类号
O61 [无机化学];
学科分类号
070301 ; 081704 ;
摘要
The bis(dihydrogen) complex RuH2(eta(2)-H-2)(2)(PCy3)(2) (1) reacts at room temperature with 1 equiv of either HBpin or HBcat to produce the a-borane complexes RuH2(eta(2)-HBpin)(eta(2)-H-2)(PCy3)(2) (2Bpin) and RuH2(eta(2)-HBcat)(eta(2)-H-2)(PCy3)(2) (2Bcat), respectively, by substitution of one sigma-H-2 ligand by one sigma-B-H. In contrast, when using the 9-BBN reagent, the dihydridoborate complex RuH[(mu-H)(2)BBN](eta(2)-H-2)(PCy3)(2) (2BBN) is formed. The coordination modes of the borane ligands have been ascertained by NMR spectroscopy, X-ray diffraction, and theoretical studies (DFT/B3LYP). The results indicate that the dialkoxyborane ligands (HBpin and HBcat) are not acidic enough to stabilize a "true" symmetrical dihydridoborate coordination mode. They thus lead to a-borane complexes presenting a small H/BH cis interaction between the boron atom and the adjacent hydride. The sigma-H-2 ligand in 2Bpin is located by X-ray diffraction at 90 K and found to be perpendicular to the equatorial plane. DFT calculations lead to the optimization of the two degenerate isomers RuH2[eta(2)-HB(OCH2)(2)](eta(2)-H-2)(PMe3)(2) (5Bpin_a) (analogous to 2Bpin) and RuH[(mu-H)(2)B(OCH2)(2)](eta(2)-H-2)(PMe3)(2) (5Bpin_b), demonstrating that sigma-H-2 rotation and sigma-borane versus dihydridoborate ligation are intimately correlated. In contrast, the 9-BBN reagent is a strong Lewis acid and leads to a dihydridoborate complex. The theoretical study on RuH[(mu-H)(2)Bpin](eta(2)-HBpin)(PCy3)(2) (3Bpin) shows that the bonding is also dependent on the hydride basicity: the RuH[(mu-H)(2)B(OCH2)(2)](PMe3)(2) fragment used as a model for RuH[(mu-H)2Bpin](PCy3)2 is not basic enough to contain a second ligand bound in a dihydridoborate mode, despite the stabilization that should be gained from the resulting symmetrical structure.
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页码:2935 / 2943
页数:9
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