IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

An overview of structurally characterized molecular organozinc hydrides is given. The compounds are presented based on the type of supporting ligand. Their synthesis, structure, reactivity, and catalytic applications are summarized in this overview. © 2015 Elsevier B.V.

Department Of Chemistry

World University root node

Coordination Chemistry Reviews

Molecular zinc hydrides

The two-coordinate germanium cation [(IDipp){(Me3Si)2CH}Ge:]+ has been synthesized, which lacks π-donor stabilization of the metal center and consequently has a very small HOMO–LUMO gap (187 kJ mol−1). It undergoes a variety of facile oxidative bond-forming reactions, most notably allowing access to the first examples of Group 14 metal cations containing ME multiple bonds (E=C, N). The use of an electrostatic (rather than purely steric) strategy to discourage aggregation means that less bulky systems (for example, containing a primary alkylidene fragment, CHR) are accessible.

German Chemical Society

Exploiting Electrostatics To Generate Unsaturation: Oxidative GeE Bond Formation Using a Non π-Donor Stabilized [R(L)Ge:]+
 Cation

A series of single component FLPs has been investigated for small molecule capture, with the finding that through tuning of both the thermodynamics of binding/activation and the degree of preorganization (i.e., ΔS⧧) reversibility can be brought about at (or close to) room temperature. Thus, the dimethylxanthene system {(C6H4)2(O)CMe2}(PMes2)(B(C6F5)2): (i) heterolytically cleaves dihydrogen to give an equilibrium mixture of FLP and H2 activation product in solution at room temperature and (ii) reversibly captures nitrous oxide (uptake at room temperature, 1 atm; release at 323 K).

Fulltext

American Chemical Society

Facile Reversibility by Design: Tuning Small Molecule Capture and Activation by Single Component Frustrated Lewis Pairs

The Third Workshop on Benchmark Problems for Airframe Noise Computations, BANC- III, was held on 14-15 June 2014 in Atlanta, Georgia, USA. The objective of this workshop was to assess the present computational capability in the area of physics-based prediction of different types of airframe noise problems and to advance the state-of-the-art via a combined effort. This documentation summarizes the results from workshop category 1 which focuses on the prediction of broadband turbulent boundary-layer trailing-edge noise and related source quantities. Since the forerunner BANC-II workshop identified some room for improvements in the achieved prediction quality BANC-III relies on the same test cases, namely 2D NACA0012 and DU96-W-180 airfoil sections in a uniform flow. Compared to BANC-II particularly the scatter among predictions for the DU96-W- 180 test case could be significantly reduced. However, proposed adaptations of previously applied computational methods did not systematically improve the prediction quality for all requested parameters. The category 1 workshop problem remains a challenging simulation task due to its high requirements on resolving and modeling of turbulent boundary-layer source quantities. © 2015, American Institute of Aeronautics and Astronautics Inc, AIAA. All Rights Reserved.

Department Of Biotechnology

21st AIAA/CEAS Aeroacoustics Conference

Broadband trailing-edge noise predictions— overview of BANC-III results

Methylene-linked bis(N,N′-di-tert-butylimidazol-2-ylidene) 1 reacted with diethylzinc to give dinuclear zinc ethyl compound 2, which contains a formally anionic bis(carbene) ligand as a result of deprotonation of the methylene bridge. The reaction of 2 with PhSiH3 gave the phenylsilyl compound 3. The zinc hydride 4 was obtained by the reaction of 2 with LiAlH4 or Ph3SiOH followed by treatment with PhSiH3. X-ray diffraction studies show that compounds 2, 3, and 4 all have a similar dimeric structure with D2h symmetry. The reaction of hydride 4 with carbon dioxide and N,N′-diisopropylcarbodiimide gave formato (5) and formamidinato (7) derivatives as a result of the insertion of the heterocumulene into both ZnH bonds. Reaction with Ph2CO gave the diphenylmethoxy compound 6. Hydride 4 shows catalytic activity in the hydrosilylation of 1,1-diphenylethylene and methanolysis of silanes.

Asian Journal

Dinuclear Zinc Hydride Supported by an Anionic Bis(N-Heterocyclic Carbene) Ligand

The (NNNN)-type macrocycle 1,4,7-trimethyl-1,4,7,10-tetraazacyclododecane (Me3TACD, 1,4,7-Me3[12]aneN4) reacted with 1 equiv of ZnEt2 under ethane elimination to give the mononuclear ethyl complex [(Me3TACD)ZnEt] (1). Upon treatment of (Me3TACD)H with 2 equiv of ZnEt2, the dinuclear complex [(Me 3TACD)(ZnEt)(ZnEt2)] (2) was formed, which was converted with an additional 1 equiv of (Me3TACD)H to 1. Reaction of 1 with PhSiH3 led to the formation of a tetranuclear ethyl hydrido complex [(Me3TACD)ZnEt2(ZnEtH)2] (3). Single-crystal X-ray diffraction study revealed 3 to be a centrosymmetric dimer featuring two [(Me3TACD)ZnEt] units coordinated to a [Zn(μ-H)2Zn] core via amido nitrogen atoms of the Me3TACD ligands. Substitution of the two [(Me3TACD)ZnEt] units in 3 by N-heterocyclic carbene IMes [1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene] gave [(IMes)ZnEtH] 2 (4b). The mixed alkyl hydrido complexes [(IMes)ZnRH]2 (R = Me, 4a; Et, 4b) were alternatively synthesized in quantitative yield by reacting [(IMes)ZnR2] (R = Me, Et) with [(IMes)ZnH2] 2 in 2:1 ratio. Methyl complex 4a reacted with CO2 (p(CO2) = 0.5 bar) under facile insertion of CO2 into Zn-H bonds to give dinuclear formate complex [(IMes)ZnMe(O2CH)] 2 (5a). Treatment of 4b with CO2 (p(CO2) = 0.5 bar) afforded a mixture of di- and trinuclear formate complexes [(IMes)ZnEt(O2CH)]2 (5b) and [(IMes)2Zn 3Et3(O2CH)3] (6) under elimination of one IMes as CO2 adduct IMes·CO2. © 2014 American Chemical Society.

Organometallics

Mixed alkyl hydrido complexes of zinc: Synthesis, structure, and reactivity

The trinuclear cationic zinc hydride cluster [(IMes)3Zn3H4 (THF)](BPh4)2 (1) was obtained either by protonation of the neutral zinc dihydride [(IMes)ZnH2]2 with a Brønsted acid or by addition of the putative zinc dication [(IMes)Zn(THF)] 2+. A triply bridged thiophenolato complex 2 was formed upon oxidation of 1 with PhS-SPh. Protonolysis of 1 by methanol or water gave the corresponding trinuclear dicationic derivatives. At ambient temperature, 1 catalyzed the hydrosilylation of aldehydes, ketones, and nitriles. Carbon dioxide was also hydrosilylated under forcing conditions when using (EtO) 3SiH, giving silylformate as the main product. © 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Angewandte Chemie - International Edition

A cationic zinc hydride cluster stabilized by an N-heterocyclic carbene: Synthesis, reactivity, and hydrosilylation catalysis

Solubility problems solved: The first examples of discrete soluble zinc dihydride adducts with NHC ligands reacted with CO2 to produce formate species and efficiently catalyzed the dehydrocoupling of silanes with methanol. These compounds were characterized both in solution and in the solid state (see picture). Copyright © 2013 WILEY-VCH Verlag GmbH &amp; Co. KGaA, Weinheim.

Molecular zinc dihydride stabilized by n-heterocyclic carbenes

The bisimidazolium salt H2-1(PF6)2 featuring a bridging 1,4-phenylene group reacts with 0.5 equiv of [PdCl(allyl)]2 in the presence of Cs2CO3 to give the dinuclear complex [2](PF6)2, whereas the reaction of the same bisimidazolium salt with 0.5 equiv of [Ir(Cl)2(Cp*)]2 yields the mononuclear orthometalated complex [3]PF6 with one remaining imidazolium unit. The unreacted imidazolium group in complex [3]PF6, however, can also be metalated with RhIII to yield the doubly orthometalated heterobimetallic complex [4]. In complex [4], each MIII center (M = IrIII and RhIII) is coordinated by one NHC unit and orthometalates the central aryl ring of the ligand.

Organomettalics

Two Different, Metal-Dependent Coordination Modes of a Dicarbene Ligand

The reaction of the benzene derived trisimidazolium salt [1](PF6)3 with [PdCl(allyl)]2 gave complex [2](PF6)3 featuring three Pd(allyl) moieties sandwiched between two tricarbene ligands, whereas the reaction of [1](PF6)3 with [M(Cp*)(Cl)2]2 (M = Ir, Rh) resulted in the formation of dinuclear MIII complexes [3]PF6 (M = Ir) and [4]PF6 (M = Rh) where each metal center is coordinated by an NHC donor and orthometallates the central phenyl ring. The remaining imidazolium group in [4]PF6 can be metallated with [Rh(Cp*)(Cl)2]2 to give the trinuclear triply orthometallated complex [5]. © 2013 The Royal Society of Chemistry.

Chemical Communications

Metal center dependent coordination modes of a tricarbene ligand

The 1,3,5-triimidazolium-substituted benzene cation in H3-1(PF6)3 reacts with Hg(OAc)2 to yield the cylinder-like trinuclear hexacarbene complex [Hg3(1)2](PF6)6. Reaction of imidazole with 1,4-dibromobenzene gives 1,4-bis(1-imidazolyl)benzene (2), which after dialkylation with ethyl bromide and salt metathesis yields the new diimidazolium salt H2-3(PF6)2. Two equivalents of H2-3(PF6)2 react with 2 equiv of Ag2O to give the dinuclear AgI tetracarbene complex [Ag2(3)2](PF6)2, which after transmetalation with [AuCl(SMe2)] yields the AuI tetracarbene complex [Au2(3)2](PF6)2. In contrast to the formation of the tetracarbene complexes of type [M2(3)2]2+ (M = AgI, AuI), the diimidazolium salt H2-3(PF6)2 reacts with Hg(OAc)2 to yield the dinuclear HgII dicarbene complex [Hg2(OAc)2(3)](PF6)2, where each mercury center is coordinated by one carbene carbon atom and one acetate oxygen atom. The crystal structure of [Hg2(OAc)2(3)](PF6)2 reveals that the complex forms a coordination polymer via intra- and intermolecular acetate bridges between HgII centers.

Polynuclear Architectures with Di- and Tricarbene Ligands

The synthesis of cylinder-type carbene complexes from polycarbene ligands and coinage metal ions via metal-controlled self-assembly has been explored. Imidazole reacts with 1,2,4,5-tetrabromobenzene or 1,3,5-tribromobenzene to give 1,2,4,5-tetrakis(1-imidazolyl)benzene (1) and 1,3,5-tris(1-imidazolyl)benzene (3), respectively. The tetrakisimidazolium salts of type H4-2a,b(Br) 4 and the trisimidazolium salts of type H3-4a,b(Br) 3 have been prepared by alkylation of the remaining free imines of the tetrakis- and trisimidazoles (H4-2a4+, H 3-4a3+: R = n-butyl; H4-2b4+, H 3-4b3+: R = ethyl). Polyimidazolium salts H 4-2a,b(PF6)4 and H3-4a,b(PF 6)3 have been synthesized by anion exchange from H 4-2a,b(Br)4 and H3-4a,b(Br)3. Two equivalents of tetraimidazolium salt H4-2a(Br)4 or H 4-2a,b(PF6)4 reacts with four equivalents of Ag2O to yield via self-assembly molecular cylinders of type [Ag 4(2a)2]Y4 (Y- = [AgBr 2]- and/or Br-) or [Ag4(2a,b) 2](PF6)4, respectively. Similarly, reaction of two equivalents of trisimidazolium salts H3-4a(Br)3 or H3-4a,b)(PF6)3 with three equivalents of Ag2O yields the molecular cylinder [Ag3(4a) 2](Y)3 (Y- = [AgBr2]- and/or Br-) or [Ag3(4a,b)2](PF 6)3, respectively. Transmetalation of [Ag 4(2a,b)2](PF6)4 with four equivalents of [AuCl(SMe2)] leads to the formation of the tetranuclear gold(I) complex [Au4(2a,b)2](PF 6)4 with retention of the metallosupramolecular assembly. Analogously, transmetalation of [Ag3(4a,b)2](PF 6)3 with three equivalents of [AuCl(SMe2)] or CuBr yields the trinuclear gold(I) complexes [Au3(4a,b) 2](PF6)3 or the copper(I) complexes [Cu 3(4a,b)2](PF6)3, respectively. Contrary to the metallosupramolecular assemblies of type [M4(2a) 2]4+ (M = Ag+, Au+), tetrakisimidazolium salt H4-2a(Br)4 reacts with K 2PtCl4 in the presence of NaOAc to yield the square-planar dinuclear complex [Pt2(2a)Br4]. © 2010 American Chemical Society.

Supramolecular structures from polycarbene ligands and transition metal ions

Tris- and tetrakis(imidazolium) salts react with Ag2O to give cylindrical polynuclear silver(I) complexes such as the tetrasilver derivative [Ag4(1)2](PF6)4. The silver(I) complexes undergo transmetalation with [AuCl(SMe2)] to yield homonuclear gold(I) complexes with retention of the metallosupramolecular assembly.