Nitrene Group Transfer Research Articles

Cobalt Silylenes as Platforms for Catalytic Nitrene‐Group Transfer by Metal–Ligand Cooperation.

A powerful approach to cooperative group-transfer catalysis is demonstrated using the Co=Si bond of a cobalt silylene to provide two distinct sites for substrate activation. The orthogonal selectivity of the Co and Si centers enables efficient nitrene-group transfer to carbon monoxide by avoiding poisoning that would result from substrates competing for a single reactive site.

Aziridination of olefins mediated by a [CuI(L1)2]+ complex via nitrene transfer reaction

Copper-catalyzed aziridination of alkenes is dominated in the literature compared to any other metal catalysts. This catalytic reaction is believed to be mediated by the elusive Cu-nitrene intermediate. However, analytical characterization of this intermediate is extremely scarce in the literature. In this article, we intend to shed the light on the electronic structure of the Cu-nitrene intermediate. The reaction of Cu(I) salt in the presence of the redox-active bidentate Schiff base ligand (C21H20N2; L1) led us to isolate a monomeric copper(I) complex with the molecular formula of [Cu(L1)2]ClO4. 2C6H6 (1), which was structurally characterized. 1 behaves as an excellent catalyst that promotes the nitrene group transfer to the variety of alkenes in the presence of (N-(p-tolylsulfonyl)imino)phenyliodinane (PhINTs). The intermediate generated from 1 by the addition of PhINTs shows an m/z peak at 832.3079 g/mol which corresponds to an M+ ion peak of the intermediate with the molecular formula of [(L1)2CuII-NTs]+ (where Ts = Tosyl). Further, based on the detailed experimental studies (in-situ UV–Vis measurement and X-band EPR measurements) we propose that the active catalyst that possesses the copper ion in its +2 oxidation state under our experimental condition, whose electronic structure can be best described as [(L1)2CuII-NTs]+ nitrene radicals. The optimized structure of the Cu-nitrene intermediate suggests that the triplet state was found to be the ground state. Besides, we propose a mechanism for this catalytic reaction.

Effects of 2,6‐Dichlorophenyl Substituents on the Coordination Chemistry of Pyridine Dipyrrolide Iron Complexes

AbstractA series of iron complexes featuring the pyridine dipyrrolide (PDP) pincer ligand [Cl2PhPDPPh]2−, obtained via deprotonation of 2,6‐bis(5‐(2,6‐dichlorophenyl)‐3‐phenyl‐1H‐pyrrol‐2‐yl)pyridine, H2Cl2PhPDPPh, is reported and structurally and spectroscopically characterized. While the bis‐pyridine adduct (Cl2PhPDPPh)Fe(py)2 exhibits nearly identical features as previously reported (MesPDPPh)Fe(py)2 (H2MesPDPPh=2,6‐bis(5‐(2,4,6‐trimethylphenyl)‐3‐phenyl‐1H‐pyrrol‐2‐yl)pyridine), the diethyl ether and tetrahydrofuran adducts (Cl2PhPDPPh)Fe(OEt2) and (Cl2PhPDPPh)Fe(thf) show additional weak Fe−Cl interactions that impact the overall coordination geometries and result in strong deviations from planar coordination environments. The reaction of (Cl2PhPDPPh)Fe(thf) with 1‐adamantyl azide provided the isolable iron imido complex (Cl2PhPDPPh)Fe(N1Ad), highlighting the improved stability of [Cl2PhPDPPh]2− towards intramolecular nitrene group transfer from the high‐valent iron‐imido unit. The electronic structure of (Cl2PhPDPPh)Fe(N1Ad) was investigated by density functional theory (DFT) and complete active space self‐consistent field (CASSCF) calculations. These computational studies suggest energetically close‐lying diamagnetic and paramagnetic states and help to conceptualize the unusual magnetic properties of the complex observed by variable‐temperature 1H NMR spectroscopy.

C–H Amination Mediated by Cobalt Organoazide Adducts and the Corresponding Cobalt Nitrenoid Intermediates

Treatment of (ArL)CoBr (ArL = 5-mesityl-1,9-(2,4,6-Ph3C6H2)dipyrrin) with a stoichiometric amount of 1-azido-4-(tert-butyl)benzene N3(C6H4-p-tBu) furnished the corresponding four-coordinate organoazide-bound complex (ArL)CoBr(N3(C6H4-p-tBu)). Spectroscopic and structural characterization of the complex indicated redox innocent ligation of the organoazide. Slow expulsion of dinitrogen (N2) was observed at room temperature to afford a ligand functionalized product via a [3 + 2] annulation, which can be mediated by a high-valent nitrene intermediate such as a CoIII iminyl (ArL)CoBr(•N(C6H4-p-tBu)) or CoIV imido (ArL)CoBr(N(C6H4-p-tBu)) complex. The presence of the proposed intermediate and its viability as a nitrene group transfer reagent are supported by intermolecular C-H amination and aziridination reactivities. Unlike (ArL)CoBr(N3(C6H4-p-tBu)), a series of alkyl azide-bound CoII analogues expel N2 only above 60 °C, affording paramagnetic intermediates that convert to the corresponding Co-imine complexes via α-H-atom abstraction. The corresponding N2-released structures were observed via single-crystal-to-crystal transformation, suggesting formation of a Co-nitrenoid intermediate in solid-state. Alternatively, the alkyl azide-bound congeners supported by a more sterically accessible dipyrrinato scaffold tBuL (tBuL = 5-mesityl-(1,9-di-tert-butyl)dipyrrin) facilitate intramolecular 1,3-dipolar cycloaddition as well as C-H amination to furnish 1,2,3-dihydrotriazole and substituted pyrrolidine products, respectively. For the C-H amination, we observe that the temperature required for azide activation varies depending on the presence of weak C-H bonds, suggesting that the alkyl azide adducts serve as viable species for C-H amination when the C-H bonds are (1) proximal to the azide moiety and (2) sufficiently weak to be activated.

Elusive Terminal Copper Arylnitrene Intermediates

AbstractWe report herein three new modes of reactivity between arylazides N3Ar with a bulky copper(I) β‐diketiminate. Addition of N3ArX3 (ArX3=2,4,6‐X3C6H2; X=Cl or Me) to [iPr2NN]Cu(NCMe) results in triazenido complexes from azide attack on the β‐diketiminato backbone. Reaction of [iPr2NN]Cu(NCMe) with bulkier azides N3Ar leads to terminal nitrenes [iPr2NN]Cu]=NAr that dimerize via formation of a C−C bond at the arylnitrene p‐position to give the dicopper(II) diketimide 4 (Ar=2,6‐iPr2C6H3) or undergo nitrile insertion to give diazametallocyclobutene 8 (Ar=4‐Ph‐2,6‐iPr2C6H2). Importantly, reactivity studies reveal both 4 and 8 to be “masked” forms of the terminal nitrenes [iPr2NN]Cu=NAr that undergo nitrene group transfer to PMe3, tBuNC, and even into a benzylic sp3 C−H bond of ethylbenzene.

Metal-Mediated Production of Isocyanates, R3 EN=C=O from Dinitrogen, Carbon Dioxide, and R3 ECl.

A highly efficient and versatile chemical cycle has been developed for the production of isocyanates through the molecular fixation of N2 , CO2 and R3 ECl (E=C, Si, and Ge). Key steps include a 'one-pot' photolytic N-N bond cleavage of a Group 6 dinuclear dinitrogen complex with in situ trapping by R3 ECl to provide a metal terminal imido complex that can engage in simultaneous nitrene-group transfer and oxygen-atom transfer to generate an intermediate metal terminal oxo complex with release of the isocyanate product. Reaction of the oxo complex with additional equivalents of R3 ECl regenerates a metal dichloride that is the precursor for dinuclear dinitrogen starting material.

Mechanism of redox-active ligand-assisted nitrene-group transfer in a Zr(IV) complex: direct ligand-to-ligand charge transfer preferred.

The mechanism of the nitrene-group transfer reaction from an organic azide to isonitrile catalyzed by a Zr(IV) d(0) complex carrying a redox-active ligand was studied by using quantum chemical molecular-modeling methods. The key step of the reaction involves the two-electron reduction of the azide moiety to release dinitrogen and provide the nitrene fragment, which is subsequently transferred to the isonitrile substrate. The reducing equivalents are supplied by the redox-active bis(2-iso-propylamido-4-methoxyphenyl)-amide ligand. The main focus of this work is on the mechanism of this redox reaction, in particular, two plausible mechanistic scenarios are considered: 1) the metal center may actively participate in the electron-transfer process by first recruiting the electrons from the redox-active ligand and becoming formally reduced in the process, followed by a classical metal-based reduction of the azide reactant. 2) Alternatively, a non-classical, direct ligand-to-ligand charge-transfer process can be envisioned, in which no appreciable amount of electron density is accumulated at the metal center during the course of the reaction. Our calculations indicate that the non-classical ligand-to-ligand charge-transfer mechanism is much more favorable energetically. Utilizing a series of carefully constructed putative intermediates, both mechanistic scenarios were compared and contrasted to rationalize the preference for ligand-to-ligand charge-transfer mechanism.

Atom‐ and Group Transfers to MIV Oxo and Imido Complexes, (η5‐C5Me5)M[N(iPr)C(Me)N(iPr)](E) (M = Mo, W; E = O, NSiMe3): Orthogonal Generation of a MVI Terminal Nitride via Inter‐ligand Silyl Group Migration

AbstractThe group 6 MIV terminal oxo complexes, Cp*M[N(iPr)C(Me)N(iPr)](O) (Cp* = η5‐C5Me5) where M = Mo (1) and W (2) react with N3SiMe3 to provide the MVI terminal nitrido complexes, Cp*M[N(iPr)C(Me)N(iPr)](N)(OSiMe3) where M = Mo (5) and W (7), respectively. A mechanism involving nitrene group transfer to generate a MVI oxo, imido intermediate, followed by inter‐ligand silyl group transfer is proposed to account for formation of 5 and 7. Compound 7 was alternatively prepared through an orthogonal route to the same proposed intermediate involving oxygen atom transfer from N2O to the WIV terminal imido complex Cp*W[N(iPr)C(Me)N(iPr)](NSiMe3) (4). The nucleophilicity of the terminal nitride 7 was further established through methylation to provide cationic {Cp*W[N(iPr)C(Me)N(iPr)](NMe)(OSiMe3)}{I} (8).

ChemInform Abstract: Iron‐Mediated Intermolecular N‐Group Transfer Chemistry with Olefinic Substrates.

The dipyrrinato iron catalyst reacts with organic azides to generate a reactive, high-spin imido radical intermediate, distinct from nitrenoid or imido species commonly observed with low-spin transition metal complexes. The unique electronic structure of the putative group-transfer intermediate dictates the chemoselectivity for intermolecular nitrene transfer. The mechanism of nitrene group transfer was probed via amination and aziridination of para-substituted toluene and styrene substrates, respectively. The Hammett analysis of both catalytic amination and aziridination reactions indicate the rate of nitrene transfer is enhanced with functional groups capable of delocalizing spin. Intermolecular amination reactions with olefinic substrates bearing allylic C–H bonds give rise to exclusive allylic amination with no apparent aziridination products. Amination of substrates containing terminal olefins give rise exclusively to allylic C–H bond abstraction, C–N recombination occurring at the terminal C with transposition of the double bond. A similar reaction is observed with cis-β-methylstyrene where exclusive amination of the allylic position is observed with isomerization of the olefin to the trans-configuration. The high levels of chemoselectivity are attributed to the high-spin electronic configuration of the reactive imido radical intermediate, while the steric demands of the ligand enforce regioselective amination at the terminal position of linear α-olefins.

Catalytic Production of Isocyanates via Orthogonal Atom and Group Transfers Employing a Shared Formal Group 6 M(II)/M(IV) Redox Cycle

Under an atmosphere of CO, the Mo(IV) imido complex Cp*Mo[N(iPr)C(Me)N(iPr)](NSiMe3) (Cp* = η5-C5Me5) (1) serves as a catalyst for production of an isocyanate via metal-mediated nitrene group transfer in benzene solution under mild conditions (55 °C, 10 psi) according to RN3 + CO → N2 + RNCO. Mechanistic and structural studies support a catalytic cycle for nitrene group transfer involving formal Mo(II) monocarbonyl and Mo(IV) (κ2-C,N)-isocyanate intermediates. These results complement an earlier finding that catalytic production of isocyanates can alternatively proceed through oxygen-atom transfer and an isomeric Mo(IV) (κ2-C,O)-isocyanate according to N2O + CNR → N2 + RNCO.

Terminal imido rhodium complexes.

Compounds of the late transition metals with M=X multiple bonds (X=CR2, NR, O) represent a synthetic challenge, partly overcome by preparative chemists, but with noticeable gaps in the second- and third-row elements. For example, there are no isolated examples of terminal imido rhodium complexes known to date. Described herein is the isolation, characterization, and some preliminary reactivity studies of the first rhodium complexes [Rh(PhBP3)(NR)] (PhBP3=PhB{CH2PPh2}3) with a multiple and terminal Rh=N bond. These imido compounds result from reactions of organic azides with the corresponding rhodium(I) complex having a labile ligand, and display a pseudo-tetrahedral core geometry with an almost linear Rh-N-C arrangement [177.5(2)°] and a short Rh-N bond [1.780(2) Å]. We also show that the Rh=N bond undergoes protonation at the nitrogen atom or addition of H2 , and also engages in nitrene-group transfer and cycloaddition reactions.

Tungsten(II) Alkylimido Complexes from Insertion of Nitriles into Tungsten Hydride: Alkylideneamido Intermediate Stage and Nitrene Group Transfer to Isocyanide

The tetrahydrido complex [WH4(κ4-P4)] (P4 = meso-o-C6H4(PPhCH2CH2PPh2)2) reacted with aliphatic nitriles AkCN at 80 °C in toluene to afford a series of the imido complexes, [W(NCH2Ak)(κ4-P4)] (2). Similar reactions with aromatic nitriles ArCN proceeded stepwise, leading to formation of the hydrido–alkylideneamido complexes [WH(N═CHAr)(κ4-P4)] (3) at the first stage and a subsequent isomerization into the imido complexes [W(NCH2Ar)(κ4-P4)] (4). Conversion of 3 into 4 was accelerated by electron-rich Ar groups such as p-CH3OC6H4, while it was completely inhibited when Ar was the considerably electron-deficient p-CF3C6H4. An X-ray crystallographic study on 2 (Ak = p-ClC6H4CH2) and 4 (Ar = p-tolyl) has disclosed a distorted-square-pyramidal coordination geometry, in which the apical position is occupied by the imido ligand with a WII–N triple bond. An almost linear WII═N═C linkage of 3 (Ar = p-tolyl) has also been determined. Complex 2 was capable of nitrene group transfer to isocyanide to produce carbodiimide.

Designing Catalysts for Nitrene Transfer Using Early Transition Metals and Redox-Active Ligands

In this Forum Article, we discuss the use of redox-active pincer-type ligands to enable multielectron reactivity, specifically nitrene group transfer, at the electron-poor metals tantalum and zirconium. Two analogous ligand platforms, [ONO] and [NNN], are discussed with a detailed examination of their similarities and differences and the structural and electronic constraints they impose upon coordination to early transition metals. The two-electron redox capabilities of these ligands enable the transfer of organic nitrenes to tantalum(V) and zirconium(IV) metal centers despite formal d(0) electron counts. Under the correct conditions, the resulting metal imido complexes can participate in further multielectron reactions such as imide reduction, nitrene coupling, or formal nitrene transfer to an isocyanide.

Catalytic nitrene transfer by a zirconium(iv) redox-active ligand complex

Nitrene transfer catalyzed by a d0zirconium(IV) complex with a redox-active ligand is reported. The redox-active ligand, bis(2-isopropylamido-4-methoxyphenyl)amide ([NNNcat]3−), afforded zirconium(IV) complexes, [NNNcat]ZrClL2 (1a, L = THF; 1b, L = CNtBu; 1c, L = py), upon reaction with ZrCl4(THF)2. Complex 1a was oxidized by one and two electrons using PhICl2, affording [NNNsq•]ZrCl2(THF) (2) and [NNNq]ZrCl3 (3), respectively. Aryl azides reacted with 1a to afford zirconium imide dimers, including the crystallographically characterized species {[NNNq]ZrCl(μ2-p-NC6H4tBu)}2 (4). The formation of 4 is the result of the addition of an aryl nitrene to the zirconium(IV) metal center. When 1b was reacted with organoazides, the dimer was not observed, but rather the nitrene group was transferred to the isonitrile to form a carbodiimide. In the presence of excess organoazide and isonitrile, catalytic carbodiimide formation occurred, showing that a redox-active ligand and a d0 metal center can work in concert to effect nitrene group transfer reactivity.

A Two-Coordinate Nickel Imido Complex That Effects C−H Amination

An exceptionally low coordinate nickel imido complex, (IPr*)Ni═N(dmp) (2) (dmp = 2,6-dimesitylphenyl), has been prepared by the elimination of N2 from a bulky aryl azide in its reaction with (IPr*)Ni(η6-C7H8) (1). The solid-state structure of 2 features two-coordinate nickel with a linear C−Ni−N core and a short Ni−N distance, both indicative of multiple-bond character. Computational studies using density functional theory showed a Ni═N bond dominated by Ni(dπ)−N(pπ) interactions, resulting in two nearly degenerate singly occupied molecular orbitals (SOMOs) that are Ni−N π* in character. Reaction of 2 with CO resulted in nitrene-group transfer to form (dmp)NCO and (IPr*)Ni(CO)3 (3). Net C−H insertion was observed in the reaction of 2 with ethene, forming the vinylamine (dmp)NH(CH═CH2) (5) via an azanickelacyclobutane intermediate, (IPr*)Ni{N,C:κ2-N(dmp)CH2CH2} (4).

Group-Transfer Reactions of Ni(II)−Ni(II) Bridging Imido Complexes. Catalytic Formation of Carbodiimides and Isocyanates via Nitrene Transfer from Organoazides

The NHC-supported Ni(I) dimer {(IPr)Ni(μ-Cl)}2 (1; IPr = 1,3-di(2,6-di-isopropylphenyl)imidazolin-2-ylidene) yields the bridging d8−d8 imido complex {(IPr)NiCl}2(μ-NMes) (2; Mes = 2,4,6-Me3C6H2) up...

Oxygen-Atom Transfer from Carbon Dioxide to a Fischer Carbene at (PNP)Ir

Dehydrogenation of the dihydride (PNP)IrH2 with norbornylene in the presence of t-butyl methyl ether leads to formation of an iridium(I) Fischer carbene complex, (PNP)Ir C(H)OtBu, by double C-H activation and loss of H2. The square planar pincer-type carbene effects quantitative oxygen-atom transfer from CO2 (1 atm) at ambient temperature to generate t-butyl formate and (PNP)Ir-CO. The iridium carbene reacts similarly with carbonyl sulfide and phenyl isocyanate, causing sulfur-atom and nitrene-group transfer, respectively. In the absence of a hydrogen acceptor, thermolysis of (PNP)IrH2 in t-butyl methyl ether under an atmosphere of CO2 also results in the formation of (PNP)Ir-CO and oxidation of t-butyl methyl ether to t-butyl formate via an iridium carbene. Preliminary mechanistic studies indicate that these reactions proceed through an intermediate four-membered metallalactone.

Synthesis and Hydrogenation of Bis(imino)pyridine Iron Imides

Treatment of the iron bis(dinitrogen) complex, (iPrPDI)Fe(N2)2 (iPrPDI = (2,6-iPr2C6H3N=CMe)2C5H3N), with a series of aryl azides resulted in loss of 3 equiv of N2 and formation of the corresponding four-coordinate iron imide compounds, (iPrPDI)Fe(NAr). These complexes, two of which (Ar = 2,6-iPr2-C6H3 and 2,4,6-Me3-C6H2) have been characterized by X-ray diffraction, are significantly distorted from planarity. The metrical parameters in combination with Mössbauer spectroscopic and SQUID magnetic data suggest an intermediate spin iron(III) center antiferromagnetically coupled to a ligand-centered radical. Nitrene group transfer has been accomplished by addition of 1 atm of CO, yielding aryl isocyanates, ArNCO, and (iPrPDI)Fe(CO)2. Hydrogenation of the more sterically hindered members of the series furnished free aniline and the previously reported iron dihydrogen complex. Catalytic aryl azide hydrogenation has also been achieved, and the observed relative rates are consistent with N-H bond formation as the rate-determining step in aniline formation.

Synthesis and Reactions of Group 4 Imido Complexes Supported by Cyclooctatetraene Ligands

The reactions of the pseudo-two-coordinate titanium imido complexes [Ti(NtBu)(COT)] (1) (COT = η8-C8H8), [Ti(NtBu)(COT‘ ‘)] (2) (COT‘ ‘ = η8-1,4-C8H6(SiMe3)2), and [Ti(NAr)(COT)] (3) (Ar = 2,6-iPr2C6H3) with a variety of organic substrates are reported. Reaction of 1 with CO2, tBuNCO, or ArNCO and reaction of 3 with CO2 or tBuNCO afforded the organic products tBuNCO, tBuNCNtBu, tBuNCNAr, ArNCO, and ArNCNtBu, respectively, and a titanium oxo species. These reactions proceeded via an initial [2 + 2] cycloaddition to form an N,O-bound intermediate of the type [Ti{N(R)C(O)R‘}(COT)], which subsequently underwent a retrocycloaddition to give an organic product and the titanium oxo species. In contrast, reaction of 3 with ArNCO led to the formation of the N,N-bound [2 + 2] cycloaddition product [Ti{N(Ar)C(O)N(Ar)}(COT)] (7). In general, the reactions of 1 and 3 with CS2 and isothiocyanates also resulted in an initial [2 + 2] cycloaddition to form an N,S-bound intermediate of the type [Ti{N(R)C(S)R‘}(COT)], which also subsequently underwent a retrocycloaddition to give an organic product and a metal sulfide species. However, the N,S-bound compound [Ti{N(Ar)C(S)S}(COT)] (10) was stable to retrocycloaddition and was isolated. Proton transfer reactions occurred between pinacol and compounds 1−3 to form the bis(alkoxide) species [Ti{OC(Me)2C(Me)2O}(COT)] (11) (from 1 or 3) or [Ti{OC(Me)2C(Me)2O}(COT‘ ‘)] (12) (from 2) and the corresponding free amine. The reactions between 1−3 and 2 equiv of the thiols tBuSH and HS-2,4,6-iPr3C6H2 all resulted in the oxidation of the thiol to the disulfides tBuS−StBu and (2,4,6-iPr3C6H2)S−S(2,4,6-iPr3C6H2). Treatment of 1 with tBuNC in the presence of 1,3,5,7-cyclooctatetraene led to formal nitrene group transfer and the formation of the Ti(II) species [Ti(COT)(η4-C8H8)] (13) and tBuNCNtBu. The analogous reactions between 2 and 3 and tBuNC resulted in the formation of the adducts [Ti(NtBu)(COT‘ ‘)(CNtBu)] (15) and [Ti(NAr)(COT)(CNtBu)] (17), and similarly the reaction between 1 and pyridine led to the isolation of the adduct [Ti(NtBu)(COT)(py)] (19) (py = pyridine). Complex 19 was crystallographically characterized. DFT studies indicated that the interaction between pyridine and the Ti center in 19 and tBuNC and the Ti center in 17 was electrostatic in nature. Complexes of the type [Ti(NR)(COT)(AlMe3-xClx)] (R = tBu, x = 0 (20); R = Ar, x = 0 (21); R = tBu, x = 1 (22); R = Ar, x = 1 (23)) were formed through the reactions of 1 and 3 with AlMe3 and AlMe2Cl, and DFT studies indicated that they contained four-membered metallacyclic rings. Attempts to prepare monomeric zirconium imido cyclooctatetraene complexes through the reactions of [Zr2(μ-NR)2Cl4(THF)x] (R = tBu, x = 3; R = 2,6-Me2C6H3(Ar‘), x = 4) with K2COT, Li2COT‘ ‘·1.8(THF), or Li2[COT*] (COT* = 1,4-C8H6(SiMe2tBu)2) were unsuccessful. Only the crystallographically characterized dimeric species [Zr2(μ-NAr‘)2(COT‘ ‘)2] (24) was isolated.

Synthesis of a Base-Free Titanium Imido and a Transient Alkylidene from a Titanocene Dinitrogen Complex. Studies on TiNR Hydrogenation, Nitrene Group Transfer, and Comparison of 1,2-Addition Rates

The synthesis and reactivity of the end-on bound dinitrogen complex [(η5-C5H3-1,3-(SiMe3)2)2Ti]2(μ2,η1,η1-N2) is described. The solid state structure of the dinitrogen compound reveals a weakly activated end-on bound N2 ligand with an N−N bond length of 1.164(5) A. Displacement of the N2 ligand by organic azides has been used to prepare monomeric, base-free titanocene imido complexes, (η5-C5H3-1,3-(SiMe3)2)2TiNR (R = SiMe3, 2,4,6-Me3-C6H2). While unreactive toward C−H bonds, the Ti−N linkage is readily hydrogenated and participates in group transfer reactions with unsaturated organic molecules such as carbon monoxide and benzophenone. Reaction of the N2 complex with Ph2CN2 allowed isolation of (η5-C5H3-1,3-(SiMe3)2)2Ti(N2CPh2), which exists as a mixture of interconverting η2 and η1 isomers in solution. The diazoalkane complex also participates in “imido-like” reactivity, producing (η5-C5H3-1,3-(SiMe3)2)2Ti(NHNCPh2)H upon addition of H2. Changing the diazoalkane to Me3SiCHN2 resulted in isolation of the do...