Multiple Cycloaddition Reactions of Ketones with a ß-Diketiminate Al Compound.

A ß-diketiminate Al compound (1) with an exocyclic double bond reacts with two equivalents each of benzophenone and 2-benzoylpyridine in a [4+2] cycloaddition to generate bicyclic and tricyclic compounds 2 and 3, respectively. Compound 2 consists of six- and eight-membered aluminium rings, whereas 3 has two five- and one eight-membered ring. Compounds 2 and 3 were characterized by a number of analytical tools including single-crystal X-ray diffraction. The quantum mechanical calculations suggest that the dissociation of the solvent molecule from 1 would lead to an active species 1A having two 1,4-dipolar 4π electron moieties, in which the electrophilic site is the Al atom and the nucleophilic positions are polarized exocyclic and endocyclic C=C π bonds. The detailed mechanistic study shows that the dipolarophiles, benzophenone, and 2-benzoylpyridine undergo double cycloaddition with two 1,4-dipolar 4π electron moieties of 1A. Herein, the addition of one molecule of the dipolarophile promotes the addition of the second one.

Evidence for the formation of a metal alkyl intermediate in the zinc mediated intramolecular hydroamination.

A diketiminato zinc amide complex, LZnNMe2 (1) [L = CH{(CMe)2(2,6-(i)Pr2C6H3N)2}], was prepared and investigated for the catalytic hydroamination of 2,2-dimethylpent-4-en-1-amine. The reaction with the amino olefin resulted in a transamination reaction and the subsequent insertion of the olefin moiety into the metal-amide bond. However, the reaction stopped at this point providing access to the metal alkyl intermediate, LZnR (R = N[upper bond 1 start]H-CH2-CPh2-CH2-C[upper bond 1 end]H-) (2). The isolation of this primary insertion product further strengthens the widely accepted mechanism for the intramolecular hydroamination.

Oxidative addition versus substitution reactions of group 14 dialkylamino metalylenes with pentafluoropyridine.

Dialkylamino compounds of group 14 elements (Si, Ge, Sn) in the +2 oxidation state supported by benzamidinate ligands were synthesized and treated with pentafluoropyridine. Two different modes of reactivity were observed, depending on the metal atom and the basicity of the substituent at the metal. Pentafluoropyridine undergoes oxidative addition reaction at the Si(II) and Ge(II) atoms whereas at the Sn(II) atom substitution of the NMe(2) group by the para fluorine of pentafluoropyridine occurs. The C-F bond activation by the lone pair of germanium is the first report of this kind. The Sn(II) fluoride obtained has an elongated Sn-F bond length and can be used as a good fluorinating agent. The compounds were characterized by multinuclear NMR spectroscopy, mass spectrometry, elemental analysis, and X-ray structural analysis. Single crystal X-ray structural analysis of the tin fluoride shows an asymmetric dimer with weak [Formula: see text] interactions.

Elegant approach to spacer arranged silagermylene and bis(germylene) compounds.

Herein we report on the reactions of the stable LSiCl (1) and LGeCl (2) [L = PhC(NtBu)(2)] with L(1)Ge, [L(1) = CH{(C[double bond, length as m-dash]CH(2))(CMe)(2,6-iPr(2)C(6)H(3)N)(2)}] (3) to yield 1-sila-5-germylene (4) and a 1,5-bis(germylene) (5). The reactions proceed through the 1,4 nucleophilic addition of the M-Cl (M = Si or Ge) to 3 without any modification of the oxidation state although the change of the oxidation state is thermodynamically more favorable. Compounds 4 and 5 were investigated by single crystal X-ray structural analyses, multi-nuclear NMR spectroscopy, and micro-analysis. Treatment of L(1)AlMe·thf (6) with 1 resulted in the formation of the 1-sila-5-aluminium complex (7). The complex contains a Si(II) and an Al(III) atom in the molecule. All reported reactions proceed without changing the oxidation states at the metal centers.

Syntheses of group 7 metal carbonyl complexes with a stable N-heterocyclic chlorosilylene.

Two structurally characterized manganese [L(2)Mn(CO)(4)](+)[Mn(CO)(5)](-) (1) and rhenium [L(3)Re(CO)(3)](+)[ReCO)(5)](-) (2) silylene complexes were prepared in one pot syntheses by reacting 1 equivalent of Mn(2)(CO)(10) with 2 equivalents of stable N-heterocyclic chlorosilylene L {L = PhC(NtBu)(2)SiCl} and 1 equivalent of Re(2)(CO)(10) with 3 equivalents of L in toluene at room temperature. Both complexes 1 and 2 were characterized by single-crystal X-ray structural analysis, NMR and IR spectroscopy, EI-MS spectrometry, and elemental analysis.

Pentafluoropyridine as a fluorinating reagent for preparing a hydrocarbon soluble ß-diketiminatolead(II) monofluoride.

A well-designed method for the preparation of a ß-diketiminatolead(II) monofluoride has been developed using LPbNMe(2) (L = [CH{C(Me)(2,6-iPr(2)C(6)H(3)N)}(2)]) and pentafluoropyridine (C(5)F(5)N). The resulting LPbF was used for the synthesis of amidinatosilicon(II) monofluoride. Moreover the activation of a ketone was observed when the LPbF was treated with PhCOCF(3).

Formation of silicon centered spirocyclic compounds: reaction of N-heterocyclic stable silylene with benzoylpyridine, diisopropyl azodicarboxylate, and 1,2-diphenylhydrazine.

Three silicon centered spirocyclic compounds 1-3, possessing silicon fused six- and five-membered rings have been prepared by the reaction of NHSi (L) [L = CH{(C=CH(2))(CMe)(2,6-iPr(2)C(6)H(3)N)(2)}Si] with benzoylpyridine, diisopropyl azodicarboxylate, and 1,2-diphenylhydrazine, respectively, in a 1:1 ratio. The three spirocyclic compounds (1- 3) were obtained by three different pathways. The reaction of L with benzoylpyridine leads to the activation of the pyridine ring, and dearomatization occurred. Treatment of diisopropyl azodicarboxylate with L favors a [1 + 4]- rather than a [1 + 2]-cycloaddition product, and the azo compound was converted to hydrazone derivative. Finally the reaction of 1,2-diphenylhydrazine and L results in the elimination of hydrogen by activating one of the C-H bonds present in the phenyl ring. All three complexes 1- 3 were characterized by single crystal X-ray structural analysis, NMR spectroscopy, EI-MS spectrometry, and elemental analysis. In addition the optimized structures of probable products and possible intermediates were investigated using density functional theory (DFT) calculations.

Chemistry of soluble ß-diketiminatoalkaline-earth metal complexes with M-X bonds (M=Mg, Ca, Sr; X=OH, Halides, H).

Victor Grignard's Nobel Prize-winning preparation of organomagnesium halides (Grignard reagents) marked the formal beginning of organometallic chemistry with alkaline earth metals. Further development of this invaluable synthetic route, RX+Mg→RMgX, with the heavier alkaline earth metals (Ca and Sr) was hampered by limitations in synthetic methodologies. Moreover, the lack of suitable ligands for stabilizing the reactive target molecules, particularly with the more electropositive Ca and Sr, was another obstacle. The absence in the literature, until just recently, of fundamental alkaline earth metal complexes with M-H, M-F, and M-OH (where M is the Group 2 metal Mg, Ca, or Sr) bonds amenable for organometallic reactions is remarkable. The progress in isolating various unstable compounds of p-block elements with ß-diketiminate ligands was recently applied to Group 2 chemistry. The monoanionic ß-diketiminate ligands are versatile tools for addressing synthetic challenges, as amply demonstrated with alkaline earth complexes: the synthesis and structural characterization of soluble ß-diketiminatocalcium hydroxide, ß-diketiminatostrontium hydroxide, and ß-diketiminatocalcium fluoride are just a few examples of our contribution to this area of research. To advance the chemistry beyond synthesis, we have investigated the reactivity and potential for applications of these species, for example, through the demonstration of dip coating surfaces with CaCO(3) and CaF(2) with solutions of the calcium hydroxide and calcium fluoride complexes, respectively. In this Account, we summarize some recent developments in alkaline earth metal complex chemistry, particularly of Mg, Ca, and Sr, through the utilization of ß-diketiminate ligands. We focus on results generated in our laboratory but give due mention to work from other groups as well. We also highlight the closely related chemistry of the Group 12 element Zn, as well as the important chemistry developed by other groups using the complexes we have reported. Although Mg and Ca are more abundant in living organisms, no other metal has as many biological functions as Zn. Thus Zn, the nontoxic alternative to the heavier Group 12 elements Cd and Hg, occupies a unique position ripe for further exploration.

A new entry into aluminum chemistry: [L(1)AlMe]⋠THF, a versatile building block for bimetallic and polymetallic complexes.

[L(1) AlMe]⋅THF (1; L(1) =CH[C(CH(2) )](CMe)(2,6-iPr(2) C(6) H(3) N)(2) ) is prepared by a new method to test its reactivity towards metal complexes to give heterobimetallic or polymetallic complexes. The treatment of 1 with germanium chloride ([LGeCl]), tin chloride ([LSnCl]; L=CH(CMe2,6-iPr(2) C(6) H(3) N)(2) ), bismuth amide ([1,8-C(10) H(6) (NSiMe(3) )(2) BiNMe(2) ]), and dimethyl zinc (ZnMe(2) ) gave the desired compounds with different functional groups on the aluminum center. All compounds have been thoroughly characterized by multinuclear NMR spectroscopy, EI mass spectrometry, X-ray crystallography (2, 3, and 5), and elemental analysis.

A rational design for an efficient synthesis of a monomeric tin(II) hydroxide.

Reaction of LSn(NMe(2))Fe(CO)(4) (L = CH{(CMe)(2,6-iPr(2)C(6)H(3)N)}(2)) with H(2)O gave the first example of a monomeric tin(ii) hydroxide complex LSn(OH)Fe(CO)(4).

Synthesis and characterization of alkynyl complexes of groups 1 and 2.

The synthesis of N-heterocyclic carbene adducts of alkynyl lithium and magnesium is achieved, and different degrees of association are observed. Reaction of strontium amide nacnacSrN(SiMe(3))(2)(thf) (nacnac = CH(CMe2,6-iPr(2)C(6)H(3)N)(2)) with PhC[triple bond]CH in THF yields the dimeric alkynyl complex [nacnacSr(thf)(mu-C[triple bond]CPh)](2) which shows an interesting coordination geometry around the metal center. The compound retains the THF molecules, unlike its lighter congener, even in hydrocarbon solvents.

Addition of dimethylaminobismuth to aldehydes, ketones, alkenes, and alkynes.

Bi-O chemistry: A direct regioselective route to bismuth bis(amino)naphthalene compounds, incorporating Bi-O and Bi-C bonds is described, in which an amide precursor is treated with aldehydes, ketones, alkenes, and alkynes, leading to insertion into the Bi-NMe(2) bond.

Well-defined hydrocarbon soluble strontium fluoride and chloride complexes of composition [LSr(thf)(micro-F)2Sr(thf)2L] and [LSr(thf)(micro-Cl)2Sr(thf)2L].

Reaction of LSrN(SiMe(3))(2)(thf) (L = CH(CMe-2,6-i-Pr(2)C(6)H(3)N)(2)) with Me(3)SnF and LAlCl(Me), respectively, gave the first example of a strontium mono fluoride complex [LSr(thf)(mu-F)(2)Sr(thf)(2)L] and the corresponding chloride derivative [LSr(thf)(mu-Cl)(2)Sr(thf)(2)L] .