Rory Waterman

Group-Transfer Reactions of Nickel-Carbene and -Nitrene Complexes with Organoazides and Nitrous Oxide that Form New C=N, C=O, and N=N Bonds

1-Adamantyl- and mesitylazide react with (dtbpe)Ni=CPh(2) (1; dtbpe = 1,2-bis(di-tert-butylphosphino)ethane) at ambient temperature to give the ketimines RN=CPh(2) (2a, R = Mes; 2b, R = Ad) in high yield. Kinetic studies for the reaction of 1 with N(3)Ad yield activation parameters of DeltaH(double dagger) = +8(+/-1) kcal/mol and DeltaS(double dagger) = -44(+/-3) cal/(mol.K). Treatment of 1 with N(2)O at low temperature results in clean conversion to the benzophenone complex (dtbpe)Ni(eta(2)-OCPh(2)) (5) upon elimination of N(2). The nickel-imido complexes (dtbpe)Ni=NR (4a, R = Mes; 4b, R = Ad) react with N(3)Mes and N(3)Ad at ambient temperature to give the diazenes RN=NR (6a, R = Mes; 6b, R = Ad) in good yield. B3LYP/6-311+G(d) calculations support a mechanism for all three reactions that features 1,3-dipolar cycloaddition to give five-membered ring (Huisgen) intermediates, followed by N(2) elimination to give the products. Calculated activation parameters for the reaction of (dhpe)Ni=CH(2) (dhpe = 1,2-bis(dihydridophosphino)ethane) with N(3)Me compare well with the experimental values.

η2-Organoazide Complexes of Nickel and Their Conversion to Terminal Imido Complexes via Dinitrogen Extrusion

1-Adamantyl- and mesitylazide react with [(dtbpe)Ni]2(eta2-mu-C6H6) to give the eta2 organic azide adducts (dtbpe)Ni(eta2-N3R) (R = Ad, 3a; Mes, 3b) that have been isolated in good yields and crystallographically characterized. These azide adducts are intermediates in the formation of the corresponding terminal imido complexes (dtbpe)NiNR (R = Ad, 4a; Mes, 4b), undergoing intramolecular loss of dinitrogen upon mild thermolysis.

Dehydrogenative Bond-Forming Catalysis Involving Phosphines

This review presents developments in the young field of dehydrogenative coupling reactions of phosphines. Catalytic phosphorus-element bond formation via dehydrocoupling has rapidly expanded since the first discoveries in the mid 1990s. A survey of the available catalysts, P-P and P-E products, and mechanistic understanding is presented with emphasis on the emerging synthetic applications of this reaction.

Intermolecular Zirconium-Catalyzed Hydrophosphination of Alkenes and Dienes with Primary Phosphines

Catalytic hydrophosphination of terminal alkenes and dienes with primary phosphines (RPH2; R = Cy, Ph) under mild conditions has been demonstrated using a zirconium complex, [κ(5)-N,N,N,N,C-(Me3SiNCH2CH2)2NCH2CH2NSiMe2CH]Zr (1). Exclusively anti-Markovnikov functionalized products were observed, and the catalysis is selective for either the secondary or tertiary phosphine (i.e., double hydrophosphination) products, depending on reaction conditions. The utility of the secondary phosphine products as substrates for further elaboration was demonstrated with a platinum-catalyzed asymmetric alkylation reaction.

A Hydrogen-Substituted Osmium Stannylene Complex : Isomerization to a Metallostannylene Complex via an Unusual α-Hydrogen Migration from Tin to Osmium

An osmium complex bearing a terminal hydrogen-substituted stannylene ligand, Cp*((i)Pr(3)P)(H)Os=SnH(trip) (1) (trip = 2,4,6-triisopropylphenyl), has been prepared by stannylene extrusion, and the complex has been structurally characterized. Complex 1 coordinates Lewis bases and activates the O-H bonds of water and methanol. Most interestingly, 1 converts to the metallostannylene complex Cp*((i)Pr(3)P)(H)(2)OsSn(trip) (2) thermally or photochemically by what appears to be a radical process.

Challenges in Catalytic Hydrophosphination

Despite significant advances, metal-catalyzed hydrophosphination has ample room for discovery, growth, and development. Many of the key successes in metal-catalyzed hydrophosphination over the last decade have indicated what is needed and what is yet to come. Reactivity that is absent from the literature also speaks to the challenges in catalytic hydrophosphination. This Concept article discusses and highlights recent developments that address the ongoing challenges, and identifies areas in metal-catalyzed hydrophosphination that are underdeveloped. Advances in product selectivity, catalyst design, and both unsaturated and phosphine substrates illustrate the ongoing development of the field. Like all catalytic transformations, the benefits are realized through catalyst, ligand, and conditions, and consideration of those features are the route to a yet more efficient and broadly applicable reaction.

Carbon–Hydrogen Bond Activation, C–N Bond Coupling, and Cycloaddition Reactivity of a Three-Coordinate Nickel Complex Featuring a Terminal Imido Ligand

The three-coordinate imidos (dtbpe)Ni=NR (dtbpe = tBu2PCH2CH2PtBu2, R = 2,6-iPr2C6H3, 2,4,6-Me3C6H2 (Mes), and 1-adamantyl (Ad)), which contain a legitimate Ni–N double bond as well as basic imido nitrogen based on theoretical analysis, readily deprotonate HC≡CPh to form the amide acetylide species (dtbpe)Ni{NH(Ar)}(C≡CPh). In the case of R = 2,6-iPr2C6H3, reductive carbonylation results in formation of the (dtbpe)Ni(CO)2 along with the N–C coupled product keteneimine PhCH=C=N(2,6- iPr2C6H3). Given the ability of the Ni=N bond to have biradical character as suggested by theoretical analysis, H atom abstraction can also occur in (dtbpe)Ni=N{2,6-iPr2C6H3} when this species is treated with HSn(nBu)3. Likewise, the microscopic reverse reaction—conversion of the Ni(I) anilide (dtbpe)Ni{NH(2,6-iPr2C6H3)} to the imido (dtbpe)Ni=N{2,6-iPr2C6H3}—is promoted when using the radical Mes*O• (Mes* = 2,4,6-tBu3C6H2). Reactivity studies involving the imido complexes, in particular (dtbpe)Ni=N{2,6-iPr2C6H3}, are also reported with small, unsaturated molecules such as diphenylketene, benzylisocyanate, benzaldehyde, and carbon dioxide, including the formation of C–N and N–N bonds by coupling reactions. In addition to NMR spectroscopic data and combustion analysis, we also report structural studies for all the cycloaddition reactions involving the imido (dtbpe)Ni=N{2,6-iPr2C6H3}.

Zirconium-Mediated Synthesis of Arsaalkene Compounds from Arsines and Isocyanides

An atom-economical synthesis of arsaalkenes via a net coupling of aryl arsines with aryl or alkyl isocyanides at zirconium is presented. Reaction of zirconium arsenido complexes (N3N)ZrAsHAr [N3N = N(CH2CH2NSiMe3)3(3-); Ar = Ph, (2) Mes (3)] with aryl and alkyl isocyanides yields arsaalkene products of the general form (N3N)Zr[NRC(H)═As(Ar)]. Two examples (5: R = Mes, Ar = Ph; 6: R = CH2Ph, Ar = Mes) were structurally characterized. Observation of intermediates in the reaction and structural characterization of the previously reported 1,1-insertion product benzylisocyanide with (N3N)ZrAsPh2 (8), (N3N)Zr[η(2)-C(PPh2)=NCH2Ph] (9), support the mechanistic hypothesis that these reactions occur via 1,1-insertion followed by rearrangement.

Synthesis, X-ray characterization, DFT calculations and Hirshfeld surface analysis of Zn(II) and Cd(II) complexes based on isonicotinoylhydrazone ligand

In this manuscript we report the synthesis and X-ray characterization of four Zn(II) complexes and three Cd(II) complexes with an asymmetrical hydrazone–pyridine based ligand {HL = 2-acetyl-pyridyl-isonicotinoylhydrazone (HAPIH)}; i.e. {[Zn(HL)2](NO3)2·H2O} (1), [Zn(HL)Br2] (2), [Zn(HL)I2] (3), [Zn(HL)(NCS)2] (4), [Cd(L)2] (5), {[Cd(HL)Br2]·CH3OH} (6) and {[Cd(HL)I2]·2CH3OH} (7). The Schiff base acts as a tridentate N2O-donor ligand through the oxygen, the imine and pyridine nitrogen atoms in all the complexes. In most complexes, the ligand is observed to coordinate as a zwitterion since the proton in the hydrazine group (N–NH–CO) shifted to the uncoordinated pyridine ring, except in 7. On the other hand, in 5 the ligand acts as a negatively charged species and is bound to the cadmium center in the enolic form (N–NC–O−). In complexes 2–4, 6 and 7, the coordination geometry around each metal center is distorted trigonal bipyramidal, with the coordination sphere of the metal completed by two halide or NCS anions. On the other hand, in homoleptic complexes 1 and 5, the metal, chelated by two tridentate Schiff base ligands, exhibits an octahedral geometry. In the crystal packing of all compounds, the pyridine rings favour π–π interactions among the symmetry related complexes. The noncovalent interactions among the complexes have been analyzed using Hirshfeld surface analysis and DFT calculations using Grimmes D3 dispersion correction to properly describe the π–π interactions.

Metal‐Ligand Cooperativity in a Methandiide‐Derived Iridium Carbene Complex

The synthesis, electronic structure, and reactivity of the first Group 9 carbene complex, [Cp*IrL] [L=C(Ph2 PS)(SO2 Ph)] (2), based on a dilithio methandiide are reported. Spectroscopic as well as computational studies have shown that, despite using a late transition-metal precursor, sufficient charge transfer occurred from the methandiide to the metal, resulting in a stable, nucleophilic carbene species with pronounced metal-carbon double-bond character. The potential of this iridium complex in the activation of a series of E-H bonds by means of metal-ligand cooperation has been tested. These studies have revealed distinct differences in the reactivity of 2 compared to a previously reported ruthenium analogue. Whereas attempts to activate the O-H bond in different phenol derivatives resulted in ligand cleavage, H-H and Si-H activation as well as dehydrogenation of isopropanol have been accomplished. These reactions are driven by the transformation of the carbene to an alkyl ligand. Contrary to a previously reported ruthenium carbene system, the dihydrogen activation has been found to proceed by a stepwise mechanism, with the activation first taking place solely at the metal. The activated products further reacted to afford a cyclometalated complex through liberation of the activated substrates. In the case of triphenylsilane, cyclometalation could thus be induced by a substoichiometric (i.e., catalytic) amount of silane.