Synthesis of Homo-Metallic Heavier Analogues of Cyclobutene and the Cyclobutadiene Dianion.

The reduction of the boryl-substituted Sn bromide {(HCDippN) B}Sn(IPrMe)Br with 1.5 equivalents of potassium graphite leads to the generation of the cyclic tetratin tetraboryl system K [Sn {B(NDippCH) } ], a homo-metallic heavier analogue of the cyclobutadiene dianion. This system is non-aromatic as determined by Nucleus Independent Chemical Shift Calculations (NICS(0)=-0.

Disproportionation and Ligand Lability in Low Oxidation State Boryl-Tin Chemistry.

Boryltin compounds featuring the metal in the+1 or 0 oxidation states can be synthesized from the carbene-stabilized tin(II) bromide (boryl)Sn(NHC)Br (boryl={B(NDippCH) }; NHC=C{(N PrCMe) }) by the use of strong reducing agents. The formation of the mono-carbene stabilized distannyne and donor-free distannide systems (boryl)SnSn(IPrMe)(boryl) (2) and K [Sn (boryl) ] (3), using Mg(I) and K reducing agents mirrors related germanium chemistry. In contrast to their lighter congeners, however, systems of the type [Sn(boryl)] are unstable with respect to disproportionation.

Reactions of a diborylstannylene with CO and NO: diboration of carbon dioxide by a main group bis(boryl) complex.

The reactions of the boryl-substituted stannylene Sn{B(NDippCH)2}2 (1) with carbon dioxide have been investigated and shown to proceed via pathways involving insertion into the Sn-B bond(s). In the first instance this leads to formation of the (boryl)tin(ii) borylcarboxylate complex Sn{B(NDippCH)2}{O2CB(NDippCH)2} (2), which has been structurally characterized and shown to feature a κ2 mode of coordination of the [(HCDippN)2BCO2]- ligand at the metal centre. 2 undergoes B-O reductive elimination in hexane solution (in the absence of further CO2) to give the boryl(borylcarboxylate)ester {(HCDippN)2B}O2C{B(NDippCH)2} (3) i.

Approaching a "Naked" Boryl Anion: Amide Metathesis as a Route to Calcium, Strontium, and Potassium Boryl Complexes.

Amide metathesis has been used to generate the first structurally characterized boryl complexes of calcium and strontium, {(Me Si) N}M{B(NDippCH) }(thf) (M=Ca, n=2; M=Sr, n=3), through the reactions of the corresponding bis(amides), M{N(SiMe ) } (thf) , with (thf) Li- {B(NDippCH) }. Most notably, this approach can also be applied to the analogous potassium amide K{N(SiMe ) }, leading to the formation of the solvent-free borylpotassium dimer [K{B(NDippCH) }] , which is stable in the solid state at room temperature for extended periods (48 h). A dimeric structure has been determined crystallographically in which the K cations interact weakly with both the ipso-carbons of the flanking Dipp groups and the boron centres of the diazaborolyl heterocycles, with K⋅⋅⋅B distances of >3.

N-H cleavage vs. Werner complex formation: reactivity of cationic group 14 tetrelenes towards amines.

β-Diketiminate ligands featuring backbone NMe groups have been exploited to access a series of two-coordinate cations of the type [(N-nacnac)E] (E = Si, Ge, Sn), whose reactivity towards N-H bonds has been investigated. While the heavier group 14 systems react via simple adduct formation, N-H oxidative addition occurs for E = Si consistent with differences in E/E redox potentials. The structurally characterized Ge/Sn adducts can be viewed as models for the corresponding (transient) Si systems [(N-nacnac)Si·(NHR)] (R = H, Bu) - which are potential intermediates in the formation of [(N-nacnac)Si(H)(NHR)]via a proton-shuttling mechanism.

Synthetic, structural and reaction chemistry of N-heterocyclic germylene and stannylene compounds featuring N-boryl substituents.

This study details the syntheses of N-heterocyclic germylenes and stannylenes featuring diazaborolyl groups, {(HCDippN)B} (Dipp = 2,6-PrCH), as both of the N-bound substituents, with a view to generating electron rich and sterically protected metal centres. The energies of their key frontier orbitals - the group 14-centred lone pair and orthogonal p-orbital (typically the HOMO-2 and LUMO) have been probed by DFT calculations and compared with a related acyclic analogue, revealing (in the case of the stannylenes) a correlation with the measured Sn chemical shifts. The reactivity of the germylene systems towards oxygen atom transfer agents has been examined, with 2 : 1 reaction stoichiometries being observed for both MeNO and pyridine N-oxide, leading to the formation of products thought to be derived from the activation of C-H bonds by a transient first-formed germanone.

Reduction of Carbon Oxides by an Acyclic Silylene: Reductive Coupling of CO.

Reactions of a boryl-substituted acyclic silylene with carbon dioxide and monoxide are reported. The former proceeds through oxygen atom abstraction, generating CO (with rearrangement of the putative silanone product through silyl-group transfer). The latter is characterized by reductive coupling of CO to give an ethynediolate fragment, which undergoes formal insertion into the Si-B bond.

A β-Diketiminate-Stabilized Sila-Acyl Chloride: Systematic Access to Base-Stabilized Silicon Analogues of Classical Carbonyl Compounds.

An oxidation/substitution strategy for the synthesis of silicon analogues of classical organic carbonyl compounds is reported, by making use of a novel β-diketiminate-supported sila-acyl chloride-the first example of such a compound isolated without the use of a stabilizing Lewis acid. Nucleophilic substitution at the Si center allows direct access to the corresponding sila-aldehyde and sila-ester. An alternative approach utilizing the reverse order of synthetic steps is thwarted by the facile rearrangement of the corresponding Si systems featuring either H or OR substituents.

Experimental and quantum chemical studies of anionic analogues of N-heterocyclic carbenes.

A combination of quantum chemical and synthetic/crystallographic methods have been employed to probe electronic structure in two series of anionic ligands related to the well known N-heterocyclic carbene (NHC) class of donor. Analyses of (i) the respective frontier orbital energies/compositions for the 'free' ligands and the results of ETS-NOCV studies of the bonding in model group 11 complexes; and (ii) the structural metrics for (new) linear gold(i) compounds, have been used to probe the bonding in complexes of NHC ligands which incorporate a backbone-appended weakly-coordinating anion component (WCA-NHCs) and in systems featuring the isoelectronic (formally anionic) diazaborolyl ligand family. Key findings are that WCA-NHC ligands - in which the anionic component is attached to the ligand heterocycle via a methylene (CH2) spacer - offer electronic (and steric) properties which are largely unperturbed from their 'simple' NHC counterparts, while diazaborolyl donors (in which the negative charge is formally located at the boron donor atom) offer significantly stronger σ-donation and a very high trans influence.

Electronic Delocalization in Two and Three Dimensions: Differential Aggregation in Indium "Metalloid" Clusters.

Reduction of indium boryl precursors to give two- and three-dimensional M-M bonded networks is influenced by the choice of supporting ligand. While the unprecedented nanoscale cluster [In (boryl) ] (with an In @In @In (boryl) concentric structure), can be isolated from the potassium reduction of a bis(boryl)indium(III) chloride precursor, analogous reduction of the corresponding (benzamidinate)In Br(boryl) system gives a near-planar (and weakly aromatic) tetranuclear [In (boryl) ] system.

New Titanium Borylimido Compounds: Synthesis, Structure, and Bonding.

We report a combined experimental and computational study of the synthesis and electronic structure of titanium borylimido compounds. Three new synthetic routes to this hitherto almost unknown class of Group 4 imide are presented. The double-deprotonation reaction of the borylamine HNB(NAr'CH) (Ar' = 2,6-CHPr) with Ti(NMe)Cl gave Ti{NB(NAr'CH)}Cl(NHMe), which was easily converted to Ti{NB(NAr'CH)}Cl(py).

Highly Electron-Rich β-Diketiminato Systems: Synthesis and Coordination Chemistry of Amino-Functionalized "N-nacnac" Ligands.

The synthesis of a class of electron-rich amino-functionalized β-diketiminato (N-nacnac) ligands is reported, with two synthetic methodologies having been developed for systems bearing backbone NMe or NEt groups and a range of N-bound aryl substituents. In contrast to their (Nacnac)H counterparts, the structures of the protio-ligands feature the bis(imine) tautomer and a backbone CH group. Direct metalation with lithium, magnesium, or aluminium alkyls allows access to the respective metal complexes through deprotonation of the methylene function; in each case X-ray structures are consistent with a delocalized imino-amide ligand description.

A Systematic Study of Structure and E-H Bond Activation Chemistry by Sterically Encumbered Germylene Complexes.

A series of new germylene compounds has been synthesized offering systematic variation in the σ- and π-capabilities of the α-substituent and differing levels of reactivity towards E-H bond activation (E=H, B, C, N, Si, Ge). Chloride metathesis utilizing [(terphenyl)GeCl] proves to be an effective synthetic route to complexes of the type [(terphenyl)Ge(ERn )] (1-6: ERn =NHDipp, CH(SiMe3 )2 , P(SiMe3 )2 , Si(SiMe3 )3 or B(NDippCH)2 ; terphenyl=C6 H3 Mes2 -2,6=Ar(Mes) or C6 H3 Dipp2 -2,6=Ar(Dipp) ; Dipp=C6 H3 iPr2 -2,6, Mes=C6 H2 Me3 -2,4,6), while the related complex [{(Me3 Si)2 N}Ge{B(NDippCH)2 }] (8) can be accessed by an amide/boryl exchange route. Metrical parameters have been probed by X-ray crystallography, and are consistent with widening angles at the metal centre as more bulky and/or more electropositive substituents are employed.

Enabling and Probing Oxidative Addition and Reductive Elimination at a Group 14 Metal Center: Cleavage and Functionalization of E-H Bonds by a Bis(boryl)stannylene.

By employing strongly σ-donating boryl ancillary ligands, the oxidative addition of H2 to a single site Sn(II) system has been achieved for the first time, generating (boryl)2SnH2. Similar chemistry can also be achieved for protic and hydridic E-H bonds (N-H/O-H, Si-H/B-H, respectively). In the case of ammonia (and water, albeit more slowly), E-H oxidative addition can be shown to be followed by reductive elimination to give an N- (or O-)borylated product.

Oxidative bond formation and reductive bond cleavage at main group metal centers: reactivity of five-valence-electron MX₂ radicals.

Monomeric five-valence-electron bis(boryl) complexes of gallium, indium, and thallium undergo oxidative M-C bond formation with 2,3-dimethylbutadiene, in a manner consistent with both the redox properties expected for M(II) species and with metal-centered radical character. The weaker nature of the M-C bond for the heavier two elements leads to the observation of reversibility in M-C bond formation (for indium) and to the isolation of products resulting from subsequent B-C reductive elimination (for both indium and thallium).

Stable GaX2, InX2 and TlX2 radicals.

The chemistry of the Group 13 metals is dominated by the +1 and +3 oxidation states, and simple monomeric M(II) species are typically short-lived, highly reactive species. Here we report the first thermally robust monomeric MX2 radicals of gallium, indium and thallium. By making use of sterically demanding boryl substituents, compounds of the type M(II)(boryl)2 (M = Ga, In, Tl) can be synthesized.

Heavy metal boryl chemistry: complexes of cadmium, mercury and lead.

Synthetic routes to the first boryl complexes of cadmium and mercury are reported via transmetallation from boryllithium; the syntheses of related group 14 systems highlight the additional factors associated with extension to more redox-active post-transition elements.

A generic one-pot route to acyclic two-coordinate silylenes from silicon(IV) precursors: synthesis and structural characterization of a silylsilylene.

Si in sight: a one-pot, single-step synthesis of an acyclic silylsilylene, Si{Si(SiMe(3))(3)}{N(SiMe(3))Dipp} (Dipp=2,6-iPr(2)C(6)H(3)), from a silicon(IV) starting material is reported, together with evidence for a mechanism involving alkali metal silylenoid intermediates.

A stable two-coordinate acyclic silylene.

Simple two-coordinate acyclic silylenes, SiR(2), have hitherto been identified only as transient intermediates or thermally labile species. By making use of the strong σ-donor properties and high steric loading of the B(NDippCH)(2) substituent (Dipp = 2,6-(i)Pr(2)C(6)H(3)), an isolable monomeric species, Si{B(NDippCH)(2)}{N(SiMe(3))Dipp}, can be synthesized which is stable in the solid state up to 130 °C. This silylene species undergoes facile oxidative addition reactions with dihydrogen (at sub-ambient temperatures) and with alkyl C-H bonds, consistent with a low singlet-triplet gap (103.

Group 3 and lanthanide boryl compounds: syntheses, structures, and bonding analyses of Sc-B, Y-B, and Lu-B σ-coordinated NHC analogues.

Reaction of [Ln(CH(2)SiMe(3))(2)(THF)(n)][BPh(4)] (Ln = Sc, Y, Lu ; n = 3, 4) with Li{B(NArCH)(2)}(THF)(2) (Ar = 2,6-C(6)H(3)(i)Pr(2)) formed the first group 3 and lanthanide boryl compounds, Sc{B(NArCH)(2)}(CH(2)SiMe(3))(2)(THF) and Ln{B(NArCH)(2)}(CH(2)SiMe(3))(2)(THF)(2) (Ln = Y, Lu), which contain two-center, two-electron Ln-B σ bonds. All of these systems were crystallographically characterized. Density functional theory analysis of the Ln-B bonding found it to be predominantly ionic, with covalent character in the σ-bonding Ln-B HOMO.

Contrasting reactivity of anionic boron- and gallium-containing NHC analogues: E-C vs. E-M bond formation (E = B, Ga).

The anionic Group 13 NHC analogues [(CHNDipp)(2)E](-) (E = B or Ga) display contrasting reactivity towards the half-sandwich titanium imido complex Cp*TiCl(NtBu)py; while the gallium system undergoes salt metathesis yielding the first example of a titanium gallyl compound, the more nucleophilic boryl anion generates a dearomatized pyridyl fragment via attack at the ligand 2-position.

Crystalline amidocerium(IV) oxides and a side-on bridging dioxygen complex.

Complexes [Ce(NR(2))(3)] (1) or [Ce(NR''(2))(3)] (2) were cerium(III) precursors to the X-ray characterised crystalline oligomeric oxygen-containing amidocerium(IV) compounds [{Ce(NR(2))(2)(mu-O)}(n)] (3, n = 2; 4, n = 3), [{Ce(NR''(2))(2)(mu-O)}(4)] (5), [{(R(2)N)(3)Ce}(2)(mu-[upper bond 1 start]OMOM[upper bond 1 end])] (6, M = Na; 7, M = K), [{(R(2)N)(3)CeOCe(NR(2))(2)}(2)(mu-[upper bond 1 start]OKOK[upper bond 1 end])] (8), and [{Ce(NR(2))(3)}(2)(mu-eta(2):eta(2)-O(2))].2C(n)H(2n+2) (9, n = 6; 9', n = 5) [R = SiMe(3), NR''(2) = TMP = [upper bond 1 start]NC(Me)(2)(CH(2))(3)C[upper bond 1 end]Me(2)]. Each was isolated in low, or for 5 very low, yield.

Crystalline di- or trianionic metal (Al, Sm) beta-diketiminates.

The new [Al(L(Tol))Br(2)] (1) and the known [Al(L(Ph))Me(2)] (2) were prepared as potential precursors to more novel aluminium compounds. In the event, only the latter was effective. Thus 2 and two equivalents of potassium was the source of [{Al(L(Ph))Me(2)K(2)(OEt(2))}(2)] (3).

Synthesis and characterisation of twelve Sn(IV) diaryls and formation of a Sn(III) triaryl.

Ten new crystalline compounds of formula (i) [{Sn(Ar(N2))(2)(micro-E)}(2)] [E = O (), S (), Se (), Te ()], (ii) [Sn(Ar(N2))(2)(ER)(2)] [ER = SCH(2)Ph (), SePh (), TePh ()], (iii) [Sn(Ar(N2))(2)(Br)R] [R = CH(SiMe(3))(2) (), Bu(t) ()] and (iv) [Sn(Ar(N2))(2){CH(SiMe(3))(2)}][BPh(4)] [Ar(N2) = C(6)H(3)(NMe(2))(2)-2,6 ()] have been prepared and identified by microanalysis, EI-mass spectrometry and multinuclear NMR spectroscopy, and for , , , and by single crystal X-ray diffraction. Whereas in the solid state, each of the latter five has only one of its two NMe(2) substituents of each [Ar(N2)](-) ligand close to the tin atom (<3.1 A), in solution at ambient temperature the NMe(2) groups are characterised by a single (1)H and (13)C signal.

Heteroleptic ytterbium(II) complexes supported by a bulky beta-diketiminato ligand.

Heteroleptic beta-diketiminatoytterbium(ii) complexes [{Yb(L)(mu-I)(thf)}(2)] [: L = {N(Ar*)C(Me)}(2)CH = L(1), : L = {N(SiMe(3))C(Ph)}(2)CH = L(2); Ar* = C(6)H(3)(i)Pr(2)-2,6] were prepared by a salt elimination [from YbI(2)(thf)(2) and KL] or by a ligand redistribution [from YbI(2)(thf)(2) and YbL(2)] reaction. Complexes and were convenient precursors to some new Yb(ii) heteroleptic compounds. Thus, reaction of and with KN(SiMe(3))(2) yielded the mononuclear amido compounds [Yb(L){N(SiMe(3))(2)}(thf)] (: L = L(1) and : L = L(2)).