Catecholborane Bound to Titanocene. Unusual Coordination of Ligand σ-Bonds

Hartwig, John F.; Muhoro, and Clare N.; He, Xiaoming; Eisenstein, Odile; Bosque, Ramón; Maseras, Feliu

doi:10.1021/ja962086v

Cited by 155 publications

(141 citation statements)

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“…Hartwig 2 ] in 1996 on the basis of NMR spectroscopy, X-ray diffraction, and MP2 calculations. [52,53] There are indeed no examples of structures incorporating a M(h 2 -C-H) 2 fragment, but it is interesting to mention some related agostic structures. The cationic iridium complex [Ir(H) 2 (PtBu 2 Ph) 2 ]…”

Section: Structures With Two S Ligandsmentioning

confidence: 99%

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The σ‐CAM Mechanism: σ Complexes as the Basis of σ‐Bond Metathesis at Late‐Transition‐Metal Centers

2007

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Complexes in which a sigma-H--E bond (E=H, B, Si, C) acts as a two-electron donor to the metal center are called sigma complexes. Clues that it is possible to interconvert sigma ligands without a change in oxidation state derive from C--H activation reactions effecting isotope exchange and from dynamic rearrangements of sigma complexes (see Frontispiece). Through these pathways, metathesis of M--E bonds can occur at late transition metals. We call this process sigma-complex-assisted metathesis, or sigma-CAM, which is distinct from the familiar sigma-bond metathesis (typical for d(0) metals and requiring no intermediate) and from oxidative-reductive elimination mechanisms (inherently requiring intermediates with changed oxidation states and sometimes involving sigma complexes). There are examples of sigma-CAM mechanisms in catalysis, especially for alkane borylation and isotope exchange of alkanes. It may also occur in silylation and alkene hydrogenation.

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Section: Structures With Two S Ligandsmentioning

confidence: 99%

“…[38,51] The first s-borane complex, which was isolated in 1996, is a titanocene complex incorporating two s-catecholborane ligands. [52] [53] Scheme 10 shows the proposed mechanism, which involves a dihydroborate intermediate.…”

Section: -H-b) and M(h 2 -H-b)(h 2 -H-si)mentioning

confidence: 99%

The σ‐CAM Mechanism: σ Complexes as the Basis of σ‐Bond Metathesis at Late‐Transition‐Metal Centers

2007

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“…[12] In the present paper we extend the previous DFT theoretical studies on [Cp 2 NbH 3 ]/BH 3 system to more realistic models of boron-based Lewis acids. [13] It is actually wellknown that BH 3 does not exist as such, but rather in a dimeric form B 2 H 6 . In the present calculations we have used two different Lewis acids that are easily prepared and have been proved experimentally to be efficient coordinating agents: a model of catecholborane and BF 3 .…”

Section: Introductionmentioning

confidence: 99%

Theoretical Study of the Effect of Lewis Acids on Dihydrogen Elimination from Niobocene Trihydrides

et al. 1999

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Dihydrogen elimination from polyhydride metallocene complexes is usually a process of high-energy cost. In this paper we study, from a theoretical point of view, the effect in the loss of dihydrogen from the niobocene [Cp 2 NbH 3 ] complex upon addition of three different Lewis acids (in increasing order of acidity: HBO 2 C 2 H 2 as a model of catecholborane, BF 3 , and BH 3 ). Our DFT calculations show that the Lewis acid can interact either with the central or the lateral hydride leading to two different minimum-energy adducts. The lateral adduct is still a dihydride complex in the HBO 2 C 2 H 2 case, whereas it shows a clear dihydrogen structure in the other two cases. This adduct is the one that leads to dihydrogen elimination. The transition states for this process show that the stronger the Lewis acid, the lower the energy barrier. In all the cases the Lewis acid favors the dihydrogen elimination process as compared with the noncatalysed H 2 elimination from the niobocene trihydride. The products are also greatly stabilized as the presence of a HBR 2 Lewis acids allow the final complex to remain coordinatively saturated upon formation of an h 2 -BH 2 R 2 complex. In BF 3 this complex cannot strictly be formed, but here the fluorine plays the role of the missing hydrogen. Finally, the implications of the different energy profiles in the kinetics of the whole process are discussed.

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“…Hartwig, [3] Sabo-Etienne, [4] and others [5] have gone a long way towards addressing this problem, by preparing a number of s-borane/borate complexes from commonly used and synthetically relevant boranes (often borabicyclononane, pinacol-or catecholborane). In many cases, the metal-ligand interaction lies at some point on a continuum comprising many subtly different bonding descriptions (for instance, situations A-C, Figure 1).…”

Section: Theconceptofthes-boraneligandisessentialtothestudyofmentioning

confidence: 99%