Crystal structure and molecular geometry of Ta(:CHCMe3)2(mesityl)(PMe3)2, a bis(alkylidene) complex of tantalum with remarkably obtuse Ta:C(.alpha.)-C(.beta.) angles of 154.0(6) and 168.9(6).degree.

Youngs, Wiley J.

doi:10.1021/ic50197a042

Cited by 28 publications

(10 citation statements)

References 7 publications

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“…These constrained angles are the result of the bridging nature of these alkylidyne ligands. The structural features around M(2) are similar to those of monomeric Ta(CH t Bu) 2 (mesityl)(PMe 3 ) 2 , which was reported by Schrock and structurally characterized by Churchill and their co-workers, and Ta(CHR) 2 (CH 2 R)(PMe 3 ) 2 (R = SiMe 3 ) that we reported recently 4c. In these monomeric bis(alkylidene) complexes, both alkylidene ligands occupy the equatorial sites of the TBP.…”

Section: Resultssupporting

confidence: 80%

Reactivities of a Bis(alkylidene) Complex. Synthesis of a Silyl Bis(alkylidyne) Complex and a Reaction Cycle among Symmetric Bis(alkylidyne), Bis(alkylidene), and Nonsymmetric Bis(alkylidyne) Compounds

Liu

Diminnie

et al. 1998

Organometallics

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An unstable bis(alkylidene) complex (RCH 2 ) 4 Ta 2 (dCHR) 2 (Cl) 2 (R ) SiMe 3 , 1), prepared by the addition of 2 equiv of HCl to a symmetrically bridging bis(alkylidyne) complex (RCH 2 ) 4 -Ta 2 (µ-CR) 2 (2a), decomposes through elimination of SiMe 4 to form an unstable alkylidenealkylidyne complex (RCH 2 ) 3 Ta 2 (dCHR)(tCR)(Cl) 2 (3). This conversion of an alkylidene to alkylidyne ligand was found to follow first-order kinetics with ∆H 1 q ) 14.1(0.8) kcal/mol and ∆S 1 q ) -12(3) eu. This is, to our knowledge, the second reported kinetic study of alkylidene f alkylidyne conversion, and the kinetics of this conversion is in contrast to that of (RCH 2 ) 3 TadCHR f (RCH 2 ) 4 Ta 2 (µ-CR) 2 (2a) reported earlier. Substitution of the chlorides by SiR 3 -(R ) SiMe 3 ) leads to a preferential elimination of HSiR 3 and formation of the first silyl bis(alkylidyne) complex (RCH 2 )(R 3 Si)Ta(µ-CR) 2 Ta(CH 2 R) 2 (4). Addition of excess PMe 3 to 1 produces a novel 1,1′-dimetallacyclobutadiene derivative (Me 3 P) 2 (Cl)Ta(µ-CR) 2 Ta(Cl)-(CH 2 R) 2 (5a) with two nonsymmetrically bridging alkylidyne ligands. Both bridging ligands coordinate with CdTa double bonds to the same metal atom (and with C-Ta single bonds to the other metal atom). The two bridging alkylidyne ligands in 5a, which are coordinated to one metal atom in the axial and equatorial position, respectively, are involved in an intramolecular ligand exchange. The kinetic barriers for this exchange were determined to be ∆H 2 q ) 13.6(0.4) kcal/mol and ∆S 2 q ) -5(2) eu in 5a, and ∆H 3 q ) 13.0(0.3) kcal/mol and ∆S 3 q ) -5(1) eu in 5b. Addition of 2 equiv of RCH 2 Li to replace the Cl ligands in 5a converts 5a to 2a, completing a reaction cycle 2a f 1 f 5a f 2a. (Me 3 P) 2 (RCH 2 )Ta(µ-CR) 2 Ta(Cl)-(CH 2 R) 2 (6) was identified as an intermediate in the conversion of 5a to 2a. absences, were uniquely consistent with the space group P21/ n. The structure was solved using the Siemens SHELXTL 93 (Version 5) proprietary software package. The niobium atoms were found by the Patterson method. The structure was completed by successive Fourier syntheses and refined to convergence by successive full-matrix least-squares refinements of F 2 . All non-hydrogen atoms were anisotropically refined. The hydrogen atoms were placed in calculated positions and introduced into the refinement as fixed contributors with isotropic U values of 0.08 Å 2 . Crystal, data collection, and refinement parameters are given in Table 1.

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Section: Resultssupporting

confidence: 80%

Reactivities of a Bis(alkylidene) Complex. Synthesis of a Silyl Bis(alkylidyne) Complex and a Reaction Cycle among Symmetric Bis(alkylidyne), Bis(alkylidene), and Nonsymmetric Bis(alkylidyne) Compounds

Liu

Diminnie

et al. 1998

Organometallics

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“…Complex 5a exhibits distorted trigonal bipyramidal geometry around the tantalum center, with the PMe 3 ligands occupying axial positions. The TaC bond distances of 1.947(12) and 1.962(12) Å are consistent with those observed for other alkylidene complexes of tantalum (1.998(8) and 1.95(2) Å in 4 , 1.932(7) and 1.955(7) Å in Ta(CHBu t ) 2 (mesityl)(PMe 3 ) 2 , and 1.932(9) Å in [Ta(CHBu t )(CH 2 Bu t )(PMe 3 ) 2 ] 2 (μ-N 2 ) 11 ). The metallasilacyclobutadiene ring in 5a is planar (average deviation from least-squares plane = 0.007 Å), which brings the silicon atom in close proximity to the tantalum center (TaSi distance of 2.607(3) Å); however, the fact that the metal center is formally d 0 makes any metal−silicon bonding interaction unlikely…”

supporting

confidence: 86%

Reactions of Alkyl Alkylidene Complexes with Silanes. Synthesis and Characterization of Novel Tantalum 1,1-Metallasilacyclobutadiene and Disilyl-Substituted Alkylidene Complexes

and

Xue

1997

J. Am. Chem. Soc.

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“…The agostic interaction significantly lengthens the C-H bond. All these features are typical for -agostic alkylidene moieties, as shown by experiment for electronically unsaturated dblock transition metal complexes 1,[77][78][79][80][81][82][83][84][85] and by computational studies. [86][87][88][89] In the cerium compound, the plane of the alkylidene moiety is neither parallel nor perpendicular to the CNT-Ce-CNT' plane, the angle between the two planes being 49.31°.…”

Section: <Table 1>mentioning

confidence: 83%

Existence and Stability of Lanthanide−Main Group Element Multiple Bonds. New Paradigms in the Bonding of the 4f Elements. A DFT Study of Cp₂CeZ (Z = F⁺, O, NH, CH^-, CH₂) and the Ligand Adduct Cp₂Ce(CH₂)(NH₃)

et al. 2005

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Crystal structure and molecular geometry of Ta(:CHCMe3)2(mesityl)(PMe3)2, a bis(alkylidene) complex of tantalum with remarkably obtuse Ta:C(.alpha.)-C(.beta.) angles of 154.0(6) and 168.9(6).degree.

Cited by 28 publications

References 7 publications

Reactivities of a Bis(alkylidene) Complex. Synthesis of a Silyl Bis(alkylidyne) Complex and a Reaction Cycle among Symmetric Bis(alkylidyne), Bis(alkylidene), and Nonsymmetric Bis(alkylidyne) Compounds

Reactivities of a Bis(alkylidene) Complex. Synthesis of a Silyl Bis(alkylidyne) Complex and a Reaction Cycle among Symmetric Bis(alkylidyne), Bis(alkylidene), and Nonsymmetric Bis(alkylidyne) Compounds

Reactions of Alkyl Alkylidene Complexes with Silanes. Synthesis and Characterization of Novel Tantalum 1,1-Metallasilacyclobutadiene and Disilyl-Substituted Alkylidene Complexes

Existence and Stability of Lanthanide−Main Group Element Multiple Bonds. New Paradigms in the Bonding of the 4f Elements. A DFT Study of Cp₂CeZ (Z = F⁺, O, NH, CH^-, CH₂) and the Ligand Adduct Cp₂Ce(CH₂)(NH₃)

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Crystal structure and molecular geometry of Ta(:CHCMe3)2(mesityl)(PMe3)2, a bis(alkylidene) complex of tantalum with remarkably obtuse Ta:C(.alpha.)-C(.beta.) angles of 154.0(6) and 168.9(6).degree.

Cited by 28 publications

References 7 publications

Reactivities of a Bis(alkylidene) Complex. Synthesis of a Silyl Bis(alkylidyne) Complex and a Reaction Cycle among Symmetric Bis(alkylidyne), Bis(alkylidene), and Nonsymmetric Bis(alkylidyne) Compounds

Reactivities of a Bis(alkylidene) Complex. Synthesis of a Silyl Bis(alkylidyne) Complex and a Reaction Cycle among Symmetric Bis(alkylidyne), Bis(alkylidene), and Nonsymmetric Bis(alkylidyne) Compounds

Reactions of Alkyl Alkylidene Complexes with Silanes. Synthesis and Characterization of Novel Tantalum 1,1-Metallasilacyclobutadiene and Disilyl-Substituted Alkylidene Complexes

Existence and Stability of Lanthanide−Main Group Element Multiple Bonds. New Paradigms in the Bonding of the 4f Elements. A DFT Study of Cp2CeZ (Z = F+, O, NH, CH-, CH2) and the Ligand Adduct Cp2Ce(CH2)(NH3)

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Existence and Stability of Lanthanide−Main Group Element Multiple Bonds. New Paradigms in the Bonding of the 4f Elements. A DFT Study of Cp₂CeZ (Z = F⁺, O, NH, CH^-, CH₂) and the Ligand Adduct Cp₂Ce(CH₂)(NH₃)