Reactions of Titanium Imides and Hydrazides with Boranes

Mellino, Simona; Stevenson, Laura C.; Clot, Eric; Mountford, Philip

doi:10.1021/acs.organomet.7b00477

Cited by 7 publications

(4 citation statements)

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“…The 1 H NMR spectra show singlets (1 H intensity) at characteristic chemical shifts of 10.51 and 10.43 ppm for the CCH of the azatitanacyclobutene unit. The 11 B NMR resonances (23.8 and 23.4 ppm, respectively) are consistent with borylamide groups ,, and are shifted significantly from the value of 14.9 ppm in 9 . The anti-Markovnikov (AM) type regiochemistry (so-called because this is the isomer that would give rise to that hydroamination product upon protolysis) of the [2 + 2] cycloaddition was established from HSQC and HMBC 1 H– 13 C NMR spectra.…”

Section: Resultsmentioning

confidence: 64%

“…The first group 4 borylimide was Mindiola’s 1 (Figure ), synthesized from a parent imide ((L)Ti(NH)) with 2 equivs of NaHBEt 3 . We subsequently reported the similarly serendipitous formation of Cp*Ti{MeC(N i Pr) 2 }(NBC 8 H 14 ) ( 2 , Figure ) via reductive N–NR 2 bond cleavage of Cp*Ti{MeC(N i Pr) 2 }(NNR 2 ) (R = Me or Ph) with 9-BBN. More recently, a catechol-functionalized borylimide was reported, again by Mindiola by reaction of a metalated nitride …”

Section: Introductionmentioning

confidence: 99%

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Synthesis of Titanium Borylimido Compounds Supported by Diamide-Amine Ligands and Their Reactions with Alkynes

Clough

Mountford

2018

Organometallics

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We report a combined synthetic, mechanistic, and computational (DFT) study of the synthesis of new diamide-amine-supported titanium borylimides and their reactions with TolCCH and ArFCCH (Tol = 4-C6H4Me, ArF = C6F5). Reaction of Ti{NB(NAr′CH)2}Cl2(py)3 (Ar′ = 2,6-C6H3 iPr2) with Li2N2 RNMe (N2 RNMe = MeN(CH2CH2NR)2) or Li2N2Npy (N2Npy = (2-C5H4N)CMe(CH2NSiMe3)2) afforded the borylimides Ti(N2 RNMe){NB(NAr′CH)2}(py) (R = SiMe3 (9), ArF (10), or iPr (11)) and Ti(N2Npy){NB(NAr′CH)2}(py) (21). Compounds 9 and 10 reacted with ArCCH (Ar = Tol or ArF) via [2 + 2] cycloaddition to form the azatitanacyclobutenes Ti(N2 RNMe){N{B(NAr′CH)2}C(H)C(Ar)}. In the case of R = ArF these underwent subsequent intramolecular C–F bond cleavage/C–C coupling processes. Reaction of 11 and 21 with TolCCH also formed azatitanacyclobutenes, whereas ArFCCH formed borylamide-acetylides via a C–H bond activation process which is endergonic in the case of TolCCH. On heating, these kinetic products rearranged via alkyne elimination to form the corresponding azatitanacyclobutenes as the thermodynamic outcomes.

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Section: Resultsmentioning

confidence: 64%

Section: Introductionmentioning

confidence: 99%

Synthesis of Titanium Borylimido Compounds Supported by Diamide-Amine Ligands and Their Reactions with Alkynes

Clough

Mountford

2018

Organometallics

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“…The reaction of 10 with 3 equiv of 9-BBN yielded scandium amido borohydride 35 and the DMAP→BBN adduct (Scheme ). It should be noted that although B–H···M agostic-type interactions are occasionally observed in transition metal imido chemistry, only in very few cases is the B–H bond cleaved . The related reaction between 12 and 9-BBN was also studied (Scheme ).…”

Section: Scandium Terminal Imides: Reactivitymentioning

confidence: 99%

“…19 It should be noted that although B−H•••M agostic-type interactions are occasionally observed in transition metal imido chemistry, only in very few cases is the B−H bond cleaved. 38 The related reaction between 12 and 9-BBN was also studied (Scheme 16). 39 In this case, C−H bond borylation on the ancillary ligand (L2 − ) occurred, which produced borohydride 36.…”

Section: Reactions Toward Saturated Chemical Bondsmentioning

confidence: 99%

Scandium Terminal Imido Chemistry

Chu

Chen

2018

Acc. Chem. Res.

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Research into transition metal complexes bearing multiply bonded main-group ligands has developed into a thriving and fruitful field over the past half century. These complexes, featuring terminal M═E/M≡E (M = transition metal; E = main-group element) multiple bonds, exhibit unique structural properties as well as rich reactivity, which render them attractive targets for inorganic/organometallic chemists as well as indispensable tools for organic/catalytic chemists. This fact has been highlighted by their widespread applications in organic synthesis, for example, as olefin metathesis catalysts. In the ongoing renaissance of transition metal-ligand multiple-bonding chemistry, there have been reports of M═E/M≡E interactions for the majority of the metallic elements of the periodic table, even some actinide metals. In stark contrast, the largest subgroup of the periodic table, rare-earth metals (Ln = Sc, Y, and lanthanides), have been excluded from this upsurge. Indeed, the synthesis of terminal Ln═E/Ln≡E multiple-bonding species lagged behind that of the transition metal and actinide congeners for decades. Although these species had been pursued since the discovery of a rare-earth metal bridging imide in 1991, such a terminal (nonpincer/bridging hapticities) Ln═E/Ln≡E bond species was not obtained until 2010. The scarcity is mainly attributed to the energy mismatch between the frontier orbitals of the metal and the ligand atoms. This renders the putative terminal Ln═E/Ln≡E bonds extremely reactive, thus resulting in the formation of aggregates and/or reaction with the ligand/environment, quenching the multiple-bond character. In 2010, the stalemate was broken by the isolation and structural characterization of the first rare-earth metal terminal imide-a scandium terminal imide-by our group. The double-bond character of the Sc═N bond was unequivocally confirmed by single-crystal X-ray diffraction. Theoretical investigations revealed the presence of two p-d π bonds between the scandium ion and the nitrogen atom of the imido ligand and showed that the dianionic [NR] imido ligand acts as a 2σ,4π electron donor. Subsequent studies of the scandium terminal imides revealed highly versatile and intriguing reactivity of the Sc═N bond. This included cycloaddition toward various unsaturated bonds, C-H/Si-H/B-H bond activations and catalytic hydrosilylation, dehydrofluorination of fluoro-substituted benzenes/alkanes, CO and H activations, activation of elemental selenium, coordination with other transition metal halides, etc. Since our initial success in 2010, and with contributions from us and across the community, this young, vibrant research field has rapidly flourished into one of the most active frontiers of rare-earth metal chemistry. The prospect of extending Ln═N chemistry to other rare-earth metals and/or different metal oxidation states, as well as exploiting their stoichiometric and catalytic reactivities, continues to attract research effort. Herein we present an account of our investigations into scandium terminal...

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