Intermolecular Activation of C−X (X = H, O, F) Bonds by a Ti⋮C<i>^t</i>Bu Linkage

The transient titanium alkylidyne complex (PNP)Ti⋮CtBu (PNP = N[2-P(CHMe2)2-4-methylphenyl]2-) can readily activate, in some cases regioselectively, the aromatic C−H bond of anisole and fluoro-substituted anisoles to generate titanium alkylidene complexes having a substituted aryl group. Intermolecular C−O bond activation occurs when perfluoroanisole reacts with (PNP)Ti⋮CtBu to afford the disubstituted alkylidene methoxide (PNP)TiC[tBu(C6F5)](OCH3). Likewise, intermediate (PNP)Ti⋮CtBu can also promote the intermolecular C−F activation of C6F6 and CF3C6F5 to generate disubstituted alkylidene fluorides (PNP)Ti[tBu(ArF)](F) (ArF = C6F5, C6F4CF3). In the case of Ar = C6F4CF3, the product resulting from para-aryl C−F activation was isolated. For the latter two C−F bond activation reactions, mixtures of alkylidene rotamers exist in solution. Complexes resulting from C−H, C−O, and C−F (including the rotamers for the latter reaction) activation have been characterized by single-crystal X-ray diffraction methods

Intermolecular Activation of C−X (X = H, O, F) Bonds by a Ti⋮C<i>^t</i>Bu Linkage

The transient titanium alkylidyne complex (PNP)Ti⋮CtBu (PNP = N[2-P(CHMe2)2-4-methylphenyl]2-) can readily activate, in some cases regioselectively, the aromatic C−H bond of anisole and fluoro-substituted anisoles to generate titanium alkylidene complexes having a substituted aryl group. Intermolecular C−O bond activation occurs when perfluoroanisole reacts with (PNP)Ti⋮CtBu to afford the disubstituted alkylidene methoxide (PNP)TiC[tBu(C6F5)](OCH3). Likewise, intermediate (PNP)Ti⋮CtBu can also promote the intermolecular C−F activation of C6F6 and CF3C6F5 to generate disubstituted alkylidene fluorides (PNP)Ti[tBu(ArF)](F) (ArF = C6F5, C6F4CF3). In the case of Ar = C6F4CF3, the product resulting from para-aryl C−F activation was isolated. For the latter two C−F bond activation reactions, mixtures of alkylidene rotamers exist in solution. Complexes resulting from C−H, C−O, and C−F (including the rotamers for the latter reaction) activation have been characterized by single-crystal X-ray diffraction methods

Intermolecular Activation of C−X (X = H, O, F) Bonds by a Ti⋮C<i>^t</i>Bu Linkage

The transient titanium alkylidyne complex (PNP)Ti⋮CtBu (PNP = N[2-P(CHMe2)2-4-methylphenyl]2-) can readily activate, in some cases regioselectively, the aromatic C−H bond of anisole and fluoro-substituted anisoles to generate titanium alkylidene complexes having a substituted aryl group. Intermolecular C−O bond activation occurs when perfluoroanisole reacts with (PNP)Ti⋮CtBu to afford the disubstituted alkylidene methoxide (PNP)TiC[tBu(C6F5)](OCH3). Likewise, intermediate (PNP)Ti⋮CtBu can also promote the intermolecular C−F activation of C6F6 and CF3C6F5 to generate disubstituted alkylidene fluorides (PNP)Ti[tBu(ArF)](F) (ArF = C6F5, C6F4CF3). In the case of Ar = C6F4CF3, the product resulting from para-aryl C−F activation was isolated. For the latter two C−F bond activation reactions, mixtures of alkylidene rotamers exist in solution. Complexes resulting from C−H, C−O, and C−F (including the rotamers for the latter reaction) activation have been characterized by single-crystal X-ray diffraction methods

Intermolecular Activation of C−X (X = H, O, F) Bonds by a Ti⋮C<i>^t</i>Bu Linkage

The transient titanium alkylidyne complex (PNP)Ti⋮CtBu (PNP = N[2-P(CHMe2)2-4-methylphenyl]2-) can readily activate, in some cases regioselectively, the aromatic C−H bond of anisole and fluoro-substituted anisoles to generate titanium alkylidene complexes having a substituted aryl group. Intermolecular C−O bond activation occurs when perfluoroanisole reacts with (PNP)Ti⋮CtBu to afford the disubstituted alkylidene methoxide (PNP)TiC[tBu(C6F5)](OCH3). Likewise, intermediate (PNP)Ti⋮CtBu can also promote the intermolecular C−F activation of C6F6 and CF3C6F5 to generate disubstituted alkylidene fluorides (PNP)Ti[tBu(ArF)](F) (ArF = C6F5, C6F4CF3). In the case of Ar = C6F4CF3, the product resulting from para-aryl C−F activation was isolated. For the latter two C−F bond activation reactions, mixtures of alkylidene rotamers exist in solution. Complexes resulting from C−H, C−O, and C−F (including the rotamers for the latter reaction) activation have been characterized by single-crystal X-ray diffraction methods

Intermolecular Activation of C−X (X = H, O, F) Bonds by a Ti⋮C<i>^t</i>Bu Linkage

The transient titanium alkylidyne complex (PNP)Ti⋮CtBu (PNP = N[2-P(CHMe2)2-4-methylphenyl]2-) can readily activate, in some cases regioselectively, the aromatic C−H bond of anisole and fluoro-substituted anisoles to generate titanium alkylidene complexes having a substituted aryl group. Intermolecular C−O bond activation occurs when perfluoroanisole reacts with (PNP)Ti⋮CtBu to afford the disubstituted alkylidene methoxide (PNP)TiC[tBu(C6F5)](OCH3). Likewise, intermediate (PNP)Ti⋮CtBu can also promote the intermolecular C−F activation of C6F6 and CF3C6F5 to generate disubstituted alkylidene fluorides (PNP)Ti[tBu(ArF)](F) (ArF = C6F5, C6F4CF3). In the case of Ar = C6F4CF3, the product resulting from para-aryl C−F activation was isolated. For the latter two C−F bond activation reactions, mixtures of alkylidene rotamers exist in solution. Complexes resulting from C−H, C−O, and C−F (including the rotamers for the latter reaction) activation have been characterized by single-crystal X-ray diffraction methods

Intermolecular Activation of C−X (X = H, O, F) Bonds by a Ti⋮C<i>^t</i>Bu Linkage

The transient titanium alkylidyne complex (PNP)Ti⋮CtBu (PNP = N[2-P(CHMe2)2-4-methylphenyl]2-) can readily activate, in some cases regioselectively, the aromatic C−H bond of anisole and fluoro-substituted anisoles to generate titanium alkylidene complexes having a substituted aryl group. Intermolecular C−O bond activation occurs when perfluoroanisole reacts with (PNP)Ti⋮CtBu to afford the disubstituted alkylidene methoxide (PNP)TiC[tBu(C6F5)](OCH3). Likewise, intermediate (PNP)Ti⋮CtBu can also promote the intermolecular C−F activation of C6F6 and CF3C6F5 to generate disubstituted alkylidene fluorides (PNP)Ti[tBu(ArF)](F) (ArF = C6F5, C6F4CF3). In the case of Ar = C6F4CF3, the product resulting from para-aryl C−F activation was isolated. For the latter two C−F bond activation reactions, mixtures of alkylidene rotamers exist in solution. Complexes resulting from C−H, C−O, and C−F (including the rotamers for the latter reaction) activation have been characterized by single-crystal X-ray diffraction methods

Intermolecular Activation of C−X (X = H, O, F) Bonds by a Ti⋮C<i>^t</i>Bu Linkage

The transient titanium alkylidyne complex (PNP)Ti⋮CtBu (PNP = N[2-P(CHMe2)2-4-methylphenyl]2-) can readily activate, in some cases regioselectively, the aromatic C−H bond of anisole and fluoro-substituted anisoles to generate titanium alkylidene complexes having a substituted aryl group. Intermolecular C−O bond activation occurs when perfluoroanisole reacts with (PNP)Ti⋮CtBu to afford the disubstituted alkylidene methoxide (PNP)TiC[tBu(C6F5)](OCH3). Likewise, intermediate (PNP)Ti⋮CtBu can also promote the intermolecular C−F activation of C6F6 and CF3C6F5 to generate disubstituted alkylidene fluorides (PNP)Ti[tBu(ArF)](F) (ArF = C6F5, C6F4CF3). In the case of Ar = C6F4CF3, the product resulting from para-aryl C−F activation was isolated. For the latter two C−F bond activation reactions, mixtures of alkylidene rotamers exist in solution. Complexes resulting from C−H, C−O, and C−F (including the rotamers for the latter reaction) activation have been characterized by single-crystal X-ray diffraction methods

Oxidatively Induced α-Hydrogen Abstraction. A Mild Protocol to Generate Terminal Titanium Alkylidenes Containing a β-Hydrogen

One-electron oxidation of the Ti(III) bis-isobutyl complexes (nacnac)Ti(CH2iPr)2 (1) (nacnac- = [ArNC(tBu)]2CH, Ar = 2,6-iPr2C6H3) and (PNP)Ti(CH2iPr)2 (4) (PNP- = N[2-P(CHMe2)2-4-methylphenyl]2) with AgOTf promotes exclusive α-hydrogen abstraction to provide the first structurally characterized examples of terminal group 4 alkylidenes bearing a β-hydrogen, namely, (nacnac)TiCHiPr(OTf) (2) and (PNP)TiCHiPr(OTf) (5). These complexes have been prepared and characterized by means of multinuclear NMR spectroscopy as well as single-crystal X-ray diffraction analysis. In the case of the nacnac framework, the reactive TiCHiPr motif can readily engage in an intramolecular Wittig-like rearrangement. However, the isobutylidene motif can be stabilized when supported by a more robust ancillary ligand such as PNP, which is demonstrated by the thermal resistance of 5 and the preparation of a rare example of a stable alkylidene methyl complex (PNP)TiCHiPr(Me) (6)

Intramolecular C−H Activation Reactions Derived from a Terminal Titanium Neopentylidene Functionality. Redox-Controlled 1,2-Addition and α-Hydrogen Abstraction Reactions

Alkylation of the terminal neopentylidene titanium(IV) complex (L1)TiCHtBu(OTf) (L1- = [Ar]NC(Me)CHC(Me)N[Ar], Ar = 2,6-(CHMe2)2C6H3) with LiCH2SiMe3 resulted in formation of the alkylidene−alkyl species (L1)TiCHtBu(CH2SiMe3) (1) in 82% yield. Compound 1 was fully characterized, and the molecular structure disclosed a four-coordinate titanium complex having significant α-hydrogen agostic interaction and possessing terminal alkylidene and alkyl functionalities. Attempts to alkylate (L1)TiCHtBu(OTf) with KCH2Ph in THF resulted in clean deprotonation of the methyl group attached to the β-carbon of the diketiminate ligand to form the four-coordinate titanium(IV) neopentylidene−tetrahydrofuran complex (L2)TiCHtBu(THF) (2; L22- = [Ar]NC(Me)CH(CH2)N[Ar], 64% isolated yield). Complex 2 was fully characterized and revealed a low-coordinate titanium(IV) in a C1 environment, which is supported by a chelating bis-anilide ligand. Alkylation of the alkylidene derivative (L3)TiCHtBu(OTf) (L3- = [Ar]NC(tBu)CHC(tBu)N[Ar], Ar = 2,6-(CHMe2)2C6H3) with LiCH2SiMe3 or KCH2Ph resulted in clean formation of (L3)TiCHtBu(R) (R = CH2SiMe3 (3), CH2Ph (4)). Complexes 3 and 4 were fully characterized, and the structure of 4 was determined by single-crystal X-ray diffraction studies. Complex 1 was found to decompose rapidly to several products, of which the titanacycle Ti[2,6-(CMe2)(CHMe2)C6H3]NC(Me)CHC(Me)N[2,6-(CMe2)(CHMe2)C6H3](CH2Si(Me)3) (5) and dimer [TiNAr([Ar]NC(Me)CHC(μ-CH2)CHtBu)]2 (6) were formed. Complex 5 was prepared in better yield through an independent synthesis involving Ti[2,6-(CMe2)(CHMe2)C6H3]NC(Me)CHC(Me)N[2,6-(CMe2)(CHMe2)C6H3](OTf) and LiCH2SiMe3. In THF complex 6 dissociated into the corresponding monomer (tBuHCC(CH2)CHC(CH3)N[Ar])TiNAr(THF) (8), quantitatively. Unlike complex 1, complexes 3 and 4 are kinetically more stable to intramolecular Wittig-like and C−H abstraction reactions. It was also found that one-electron reduction of the four-coordinate titanium alkylidene complexes (L1)TiCHtBu(OTf) and (L3)TiCHtBu(OTf) afforded the Ti(III) metallacycles ([Ar]NC(R)CHC(R)N[2,6-(CHMe2)(CH(CH2)(Me))C6H3])TiCH2tBu (L42-, R = Me (9); L52-, R = tBu (10)), both resulting from 1,2-addition of the proximal isopropyl CH3 group across the TiCHtBu bond. One-electron oxidation of 10 with AgOTf promotes α-abstraction to generate back the alkylidene precursor (L3)TiCHtBu(OTf). The redox-controlled 1,2-addition and α-abstraction reactions are specific only to the isopropyl methyl attached to the aryl group of the β-diketiminate ligand

Terminal Titanium(IV) (Trimethylsilyl)imides Prepared by Oxidatively Induced Trimethylsilyl Abstraction

Titanium (trimethylsilyl)imide triflate complexes of the type (L)TiNSiMe3(OTf) (L- = [ArNC(CH3)]2CH, Ar = 2,6-iPr2C6H3; L- = N[2-P(CHMe2)2-4-MeC6H3]2) can be readily prepared by one-electron oxidation and subsequent trimethylsilyl abstraction in the Ti(III) precursors (L)TiCl(N{SiMe3}2)