Erli Lu

Yttrium Anilido Hydride: Synthesis, Structure, and Reactivity

The synthesis, structure, and reactivity of the yttrium anilido hydride [LY(NH(DIPP))(mu-H)](2) (3; L = [MeC(N(DIPP))CHC(Me)(NCH(2)CH(2)NMe(2))](-), DIPP = 2,6-(i)Pr(2)C(6)H(3))) are reported. The protonolysis reaction of the yttrium dialkyl [LY(CH(2)SiMe(3))(2)] (1) with 1 equiv of 2,6-diisopropylaniline gave the yttrium anilido alkyl [LY(NH(DIPP))-(CH(2)SiMe(3))] (2), and a subsequent sigma-bond metathesis reaction of 2 with 1 equiv of PhSiH(3) offered the yttrium anilido hydride 3. The structure of 3 was characterized by X-ray crystallography, which showed that the complex is a mu-H dimer. 3 shows high reactivity toward a variety of unsaturated substrates, including imine, azobenzene, carbodiimide, isocyanide, ketone, and Mo(CO)(6), giving some structurally intriguing products.

C–P or C–H Bond Cleavage of Phosphine Oxides Mediated by an Yttrium Hydride

Reactions of the yttrium anilido hydride [LY(NH(DIPP))(mu-H)](2) (1; L = [MeC(N(DIPP))CHC(Me)(NCH2CH2NMe2)]-, DIPP = (2),6-(Pr2C6H3)-Pr-i)) with three phosphine oxides and two phosphine sulfides are reported. The reaction of 1 with Ph3P=O gives C P bond cleavage and an yttrium anilido phosphinoyl complex, while those with R2MeP=O (R = Me, Ph) result in C H bond cleavage and two yttrium anilido alkyl complexes. 1 also reacted with R3P=S (R = Me, Ph), which demonstrated P S bond cleavage via hydride-based reduction and gave an yttrium anilido sulfide.

Scandium Terminal Imido Chemistry

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]2- 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, CO2 and H2 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 imido chemistry as a timely summary, in the hope that our studies will be of interest to this readership.

Synthesis of Scandium Terminal Hydride From H2 Activation by Scandium Terminal Imido Complex and Its Reactivity

Dihydrogen is easily activated by a scandium terminal imido complex containing the weakly coordinated THF. The reaction proceeds through a 1,2-addition mechanism, which is distinct from the σ-bond metathesis mechanism reported to date for rare-earth metal-mediated H2 activation. This reaction yields a scandium terminal hydride, which is structurally well-characterized, being the first one to date. The reactivity of this hydride is reported with unsaturated substrates, further shedding light on the existence of the terminal hydride complex. Interestingly, the H2 activation can be reversible. DFT investigations further eludciate the mechanistic aspects of the reactivity of the scandium anilido-terminal hydride complex with PhNCS but also on the reversible H2 activation process.