Synthesis and EPR/UV/Vis‐NIR Spectroelectrochemical Investigation of a Persistent Phosphanyl Radical Dication

The reaction of the bis(imidazoliumyl)‐substituted P^I cation [(2‐Im^Dipp)P(4‐Im^Dipp)]⁺ ( 10 ⁺) (2‐Im=imidazolium‐2‐yl; 4‐Im=imidazolium‐4‐yl; Dipp=2,6‐di‐isopropylphenyl) with trifluoromethanesulfonic acid (HOTf) or methyl trifluoromethylsulfonate (MeOTf) yields the corresponding protonated [(2‐Im^Dipp)PH(4‐Im^Dipp)]²⁺ ( 11 ²⁺) and methylated [(2‐Im^Dipp)PMe(4‐Im^Dipp)]²⁺ ( 12 ²⁺) dications, respectively. EPR/UV/Vis‐NIR spectroelectrochemical investigation of the low‐coordinated P^I cation 10 ⁺ predicted a stable and “bottleable” P‐centered radical dication [(2‐Im^Dipp)P(4‐Im^Dipp)]^2+. ( 13 ^2+.). The reaction of 10 ⁺ with the nitrosyl salt NO[OTf] yields the persistent phosphanyl radical dication 13 ^2+. as triflate salt in crystalline form. Quantum chemical investigation revealed an exceptional high spin density at the P atom.     

Distibanes and Distibenes from Reduction of Sb(NONR)Cl by using MgI Reagents

The bis(amidodimethyl)disiloxane antimony chlorides Sb(NON^R)Cl (NON^R=[O(SiMe₂NR)₂]²⁻; R=tBu, Ph, 2,6-Me₂C₆H₃=Dmp, 2,6-iPr₂C₆H₃=Dipp, 2,6-(CHPh₂)₂-4-tBuC₆H₂=tBu-Bhp) are reduced to Sb^II and Sb^I species by using Mg^I reagents, [Mg(BDI^R′)]₂ (BDI=[HC{C(Me)NR′}₂]⁻; R′=2,4,6-Me₃C₆H₂=Mes, Dipp). Stoichiometric reactions with Sb(NON^R)Cl (R=tBu, Ph) form dimeric Sb^II stibanes [Sb(NON^R)]₂, shown crystallographically to contain Sb−Sb single bonds. The analogous distibane with R=Dmp substituents has an exceptionally long Sb−Sb interaction and exhibits spectroscopic and reactivity properties consistent with radical character in solution. When R=Dipp, reductions with Mg^I reagents directly give distibenes [Sb(μ-NON^Dipp)Mg(BDI^R′)(THF)_n]₂ (R′=Mes, n=1; R′=Dipp, n=0). Crystallographic analysis shows a trans-substitution of the Sb=Sb double bond, with bridging NON^Dipp-ligands between the Sb^I and Mg^II centres. An attempt to access the NON^Ph-analogue using the same protocol afforded the polystibide cluster Sb₈[μ₄,η^2:2:2:2-Mg(BDI^Mes)]₄, which co-crystallized with the ligand transfer product, [Mg(BDI^Mes)]₂(μ-NON^Ph).     

Seven-Membered Cyclic Potassium Diamidoalumanyls

The seven-membered cyclic potassium alumanyl species, [{SiN^Mes}AlK]₂ [{SiN^Mes}={CH₂SiMe₂N(Mes)}₂; Mes=2,4,6-Me₃C₆H₂], which adopts a dimeric structure supported by flanking K-aryl interactions, has been isolated either by direct reduction of the iodide precursor, [{SiN^Mes}AlI], or in a stepwise manner via the intermediate dialumane, [{SiN^Mes}Al]₂. Although the intermediate dialumane has not been observed by reduction of a Dipp-substituted analogue (Dipp=2,6-i-Pr₂C₆H₃), partial oxidation of the potassium alumanyl species, [{SiN^Dipp}AlK]₂, where {SiN^Dipp}={CH₂SiMe₂N(Dipp)}₂, provided the extremely encumbered dialumane [{SiN^Dipp}Al]₂. [{SiN^Dipp}AlK]₂ reacts with toluene by reductive activation of a methyl C(sp³)-H bond to provide the benzyl hydridoaluminate, [{SiN^Dipp}AlH(CH₂Ph)]K, and as a nucleophile with BPh₃ and RN=C=NR (R=i-Pr, Cy) to yield the respective Al-B- and Al-C-bonded potassium aluminaborate and alumina-amidinate products. The dimeric structure of [{SiN^Dipp}AlK]₂ can be disrupted by partial or complete sequestration of potassium. Equimolar reactions with 18-crown-6 result in the corresponding monomeric potassium alumanyl, [{SiN^Dipp}Al−K(18-cr-6)], which provides a rare example of a direct Al−K contact. In contrast, complete encapsulation of the potassium cation of [{SiN^Dipp}AlK]₂, either by an excess of 18-cr-6 or 2,2,2-cryptand, allows the respective isolation of bright orange charge-separated species comprising the ‘free’ [{SiN^Dipp}Al]⁻ alumanyl anion. Density functional theory (DFT) calculations performed on this moiety indicate HOMO-LUMO energy gaps in the of order 200–250 kJ mol⁻¹.     

Unexpected results of the reactions of manganese and vanadium β-diketiminate halide complexes with Na[HBEt3]

The reaction of [(^Menacnac^Dipp)Mn(μ-Cl)]₂(2) (^Menacnac^Dipp = HC(C(Me)NDipp)₂; Dipp = 2,6-Prⁱ₂C₆H₃) with sodium triethylborohydride in a toluene—THF mixture afforded the complex [(^Menacnac^Dipp)Mn(μ-H)₂BEt₂(THF)] (3). The reaction of 2 with Na[HBEt₃] in toluene under THF-free conditions gave a mixture of products. The set and the ratio of these products in the resulting crystalline mixture were established by quantitative powder X-ray diffraction analysis: [(^Menacnac^Dipp)Mn(μ-H)]₂(1), [(^Menacnac^Dipp)?Mn(μ-H)₂BEt₂] (4), and unreacted compound 2 in the ratio of 15:4:1 and traces of an unknown crystalline phase. The reaction of [(^Menacnac^Dipp)VCl₂] (5) with Na[HBEt₃] yielded the compound [(^Menacnac^Dipp)V(μ-H)(μ,κ^1:1?C:C′?C₂H₄)BEt₂] (6) containing the unusual ligand [HBEt₂(CH₂CH₂)]^2?. The vanadium analog of compound 3, [(^Menacnac^Dipp)V(μ-H)₂BEt₂(THF)] (7), was isolated in one experiment. Besides. a small amount of the complex [(^Menacnac^Dipp)V(μ-H)BEt₃(THF)] (8) was detected in the mixture of crystalline products. The structures of compounds 3, 4, 6, 7, and 8 were determined by single-crystal X-ray diffraction.

     

Titanium-Mediated Catalytic Hydrogenation of Monocyclic and Polycyclic Arenes

Two electron-reduction of the Ti^IV guanidinate complex (Im^DippN)(^Xyketguan)TiCl₂ gives (η⁶-Im^DippN)(^xyketguan)Ti ( 1^intra ) and (Im^DippN)(^Xyketguan)Ti(η⁶-C₆H₆) ( 1^inter ) (^Xyketguan=[(tBuC=N)C(NXylyl)₂]⁻, Xylyl=2,5-dimethylphenyl) in the absence or presence of benzene, respectively. These complexes have been found to hydrogenate monocyclic and polycyclic arenes under relatively mild conditions (150 psi, 80 °C)—the first example of catalytic, homogeneous arene hydrogenation with TON >1 by a Group IV system.     

Four‐Membered Heterometallacyclic d0 and d1 Complexes of Group 4 Metallocenes with Amidato Ligands

A study of the coordination chemistry of different amidato ligands [(R)N?C(Ph)O] (R=Ph, 2,6‐diisopropylphenyl (Dipp)) at Group 4 metallocenes is presented. The heterometallacyclic complexes [Cp₂M(Cl){κ²‐N,O‐(R)N?C(Ph)O}] M=Zr, R=Dipp ( 1 a ), Ph ( 1 b ); M=Hf, R=Ph ( 2 )) were synthesized by reaction of [Cp₂MCl₂] with the corresponding deprotonated amides. Complex 1 a was also prepared by direct deprotonation of the amide with Schwartz reagent [Cp₂Zr(H)Cl]. Salt metathesis reaction of [Cp₂Zr(H)Cl] with deprotonated amide [(Dipp)N?C(Ph)O] gave the zirconocene hydrido complex [Cp₂M(H){κ²‐N,O‐(Dipp)N?C(Ph)O}] ( 3 ). Reaction of 1 a with Mg did not result in the desired Zr(III) complex but in formation of Mg complex [(py)₃Mg(Cl) {κ²‐N,O‐(Dipp)N?C(Ph)O}] ( 4 ; py=pyridine). The paramagnetic complexes [Cp′₂Ti{κ²‐N,O‐(R)N?C(Ph)O}] (Cp′=Cp, R=Ph ( 7 a ); Cp′=Cp, R=Dipp ( 7 b ); Cp′=Cp*, R=Ph ( 8 )) were prepared by the reaction of the known titanocene alkyne complexes [Cp₂′Ti(η²‐Me₃SiC₂SiMe₃)] (Cp′=Cp ( 5 ), Cp′=Cp* ( 6 )) with the corresponding amides. Complexes 1 a , 2 , 3 , 4 , 7 a , 7 b , and 8 were characterized by X‐ray crystallography. The structure and bonding of complexes 7 a and 8 were also characterized by EPR spectroscopy.     

The Non-Ancillary Nature of Trimethylsilylamide Substituents in Boranes and Borinium Cations

The known boranes (R(Me₃Si)N)₂BF (R=Me₃Si 1 , tBu 2 , C₆F₅ 3 , o-tol 4 , Mes 5 , Dipp 6 ) and borinium salts (R(Me₃Si)N)₂B][B(C₆F₅)₄] (R=Me₃Si 7 , tBu 8 ) are prepared and fully characterized. Compound 7 is shown to react with phosphines to generate [R₃PSiMe₃]⁺ and [R₃PH]⁺ (R=Me, tBu). Efforts to generate related borinium cations via fluoride abstraction from (R(Me₃Si)N)₂BF (R=C₆F₅ 3 , o-tol 4 , Mes 5 ) gave complex mixtures suggesting multiple reaction pathways. However for R=Dipp 6 , the species [(μ-F)(SiMe₂N(Dipp))₂BMe][B(C₆F₅)₄] was isolated as the major product, indicating methyl abstraction from silicon and F/Me exchange on boron. These observations together with state-of-the-art DFT mechanistic studies reveal that the trimethylsilyl-substituents do not behave as ancillary subsitutents but rather act as sources of proton, SiMe₃ and methyl groups.     

Stable N‐Heterocyclic Germylenes of the Type [Fe{(η5‐C5H4)NR}2Ge] and Their Oxidation Reactions with Sulfur,Selenium, and Diphenyl Diselenide

Three new N‐heterocyclic germylenes of the type [Fe{(η⁵‐C₅H₄)NR}₂Ge] ( 1R Ge) containing particularly bulky alkyl [R = 2‐adamantyl (Ad), 1,1,2,2‐tetramethylpropyl (Pr*)] or aryl substituents [R = 2,6‐diisopropylphenyl (Dipp)] were prepared and structurally characterized, in two cases (R = Ad, Dipp), by single‐crystal X‐ray diffraction. Together with the previously described homologues with R = trimethylsilyl (TMS), tert‐butyl (tBu), and mesityl (Mes) their oxidative addition reactions with S₈ and Se₈ were studied, which afforded compounds of the type [ 1R Ge(μ‐E)]₂ (E = S, Se). The low solubility of most of these products severely hampered their purification and characterization. Nevertheless, their structural characterization by single‐crystal X‐ray diffraction was possible in six cases (E = S, R = Ad, Pr*; E = Se, R = Ad, Pr*, Mes, Dipp). No solubility problems were encountered in oxidative addition reactions with diphenyl diselenide, affording products of the type 1R Ge(SePh₂)₂, whose crystal structures could be determined in four cases (R = TMS, tBu, Mes, Dipp). Short intramolecular CH ··· Se contacts compatible with hydrogen bonds were observed for [ 1Ad Ge(μ‐Se)]₂, [ 1Pr* Ge(μ‐Se)]₂, and 1tBu Ge(SePh₂)₂.     

Synthesis and physiochemical studies on binuclear Cu(II) complexes derived from 2,6-[(N-phenylpiperazin-1-yl)methyl]-4-substituted phenols

Preparation of the ligands HL¹ = 2,6-[(N-phenylpiperazin-1-yl)methyl]-p-ethylphenol; HL² = 2,6-[(N-phenylpiperazin-1-yl)methyl]-p-methoxyphenol and HL³ = 2,6-[(N-phenylpiperazin-1-yl)methyl]-p-nitrophenol are described together with their Cu(II) complexes with different bridging units. The exogenous bridges incorporated into the complexes are: hydroxo [Cu₂L(OH)(H₂O)₂](ClO₄)₂.H₂O (L¹=1a, L² =1b, L³ =1c), acetato [Cu₂L(OAc)₂]ClO₄.H₂O (L¹ =2a, L² =2b, L³ =2c) and nitrito [Cu₂L¹(NO₂)₂(H₂O)₂]ClO₄.H₂O (L¹=3a, L² =3b, L³ =3c). Complexes1a,1b,1c and2a,2b,2c contain bridging exogenous groups, while3a,3b,3c possess only open μ-phenolate structures. Both the ligands and complexes were characterized by spectral studies. Cyclic voltammetric investigation of these complexes revealed that the reaction process involves two successive quasireversible one-electron steps at different potentials. The first reduction potential is sensitive to electronic effects of the substituents at the aromatic ring of the ligand system, shifting to positive potentials when the substituents are replaced by more electrophilic groups. EPR studies indicate very weak interaction between the two copper atoms. Various covalency parameters have been calculated.     

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(ER_n)] ( 1 – 6 : ER_n=NHDipp, CH(SiMe₃)₂, P(SiMe₃)₂, Si(SiMe₃)₃ or B(NDippCH)₂; terphenyl=C₆H₃Mes₂‐2,6=Ar^Mes or C₆H₃Dipp₂‐2,6=Ar^Dipp; Dipp=C₆H₃iPr₂‐2,6, Mes=C₆H₂Me₃‐2,4,6), while the related complex [{(Me₃Si)₂N}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. Thus, the widest germylene units (θ>110°) are found to be associated with strongly σ‐donating boryl or silyl ancillary donors. HOMO–LUMO gaps for the new germylene complexes have been appraised by DFT calculations. The aryl(boryl)‐germylene system [Ar^MesGe{B(NDippCH)₂}] ( 6 ‐Mes), which features a wide C‐Ge‐B angle (110.4(1)°) and (albeit relatively weak) ancillary π‐acceptor capabilities, has the smallest HOMO–LUMO gap (119 kJ mol^?1). These features result in 6 ‐Mes being remarkably reactive, undergoing facile intramolecular C?H activation involving one of the mesityl ortho‐methyl groups. The related aryl(silyl)‐germylene system, [Ar^MesGe{Si(SiMe₃)₃}] ( 5 ‐Mes) has a marginally wider HOMO–LUMO gap (134 kJ mol^?1), rendering it less labile towards decomposition, yet reactive enough to oxidatively cleave H₂ and NH₃ to give the corresponding dihydride and (amido)hydride. Mixed aryl/alkyl, aryl/amido and aryl/phosphido complexes are unreactive, but amido/boryl complex 8 is competent for the activation of E?H bonds (E=H, B, Si) to give hydrido, boryl and silyl products. The results of these reactivity studies imply that the use of the very strongly σ‐donating boryl or silyl substituents is an effective strategy for rendering metallylene complexes competent for E?H bond activation.     

Low‐Coordinate Single‐Ion Magnets by Intercalation of Lanthanides into a Phenol Matrix

It is very challenging to synthesize stable trivalent rare‐earth complexes in which the coordination number is lower than 3 for the high oxidation state, there is a large ion radius and nearly non‐bonding character of trivalent lanthanide ions. The bulky phenol ligand ArOH (Ar=2,6‐Dipp₂C₆H₃, Dipp=2,6‐diisopropylphenyl) was utilized to construct low‐coordinate lanthanide compound [(ArO)Ln(OAr′)] (Ar′=6‐Dipp‐2‐(2′‐ⁱPr‐6′‐CHMe(CH₂^?)C₆H₃)C₆H₃O^?; Ln=Tb, Dy, Ho, Er, Tm). These complexes and the free ligand ArOH were isostructural. Magnetic measurements and theoretical studies demonstrated that both the oblate‐type dysprosium and prolate‐type erbium analogues exhibited single‐ion magnet (SIM) behavior. The bulky phenol ligands provided strong uniaxial ligand field, making the dysprosium SIM possessing blocking barrier up to 961 K.     

Synthesis of Binam‐P Derived C2‐Symmetric bis‐Iminophosphonamide Ligands. Molecular Structure of [(R)‐Binam(Ph2PN(H)tBu)2]

The Staudinger reaction of organic azides tBuN₃, 1‐Ad‐N₃, and DippN₃ (Dipp = 2,6‐diisopropylphenyl) with (R)‐N,N′‐bis(diphenylphosphanyl)‐2,2′‐diamino‐1,1′‐binaphthyl [(R)‐Binam‐P], obtained by an optimized procedure from (R)‐(+)‐Binam, Ph₂PCl, and Et₃N in DCM, leads to preparation of a series of new C₂‐symmetric bis‐iminophosphonamide ligands [(R)‐Binam(Ph₂PN(H)R)₂] [R = tBu ( 1 ), Ad ( 2 ), and Dipp ( 3 )]. The molecular structure of 1· 2DMSO was confirmed by X‐ray structure analysis.     

Synthesis and reaction chemistry of 4-nitrile-substituted NCN-pincer palladium(II) and platinum(II) complexes (NCN = [NC-4-C6H2(CH2NMe2)2-2,6])

Nitrile-functionalized NCN-pincer complexes of type [MBr(NC-4-C₆H₂(CH₂NMe₂)₂-2,6)] (6a, M = Pd; 6b, M = Pt) (NCN = [C₆H₂(CH₂NMe₂)₂-2,6]⁻) are accessible by the reaction of Br-1-NC-4-C₆H₂(CH₂NMe₂)₂-2,6 (2b) with [Pd₂(dba)₃ · CHCl₃] (5a) (dba = dibenzylidene acetone) and [Pt(tol-4)₂(SEt₂)]₂ (5b) (tol = tolyl), respectively. Complex 6b could successfully be converted to the linear coordination polymer {[Pt(NC-4-C₆H₂(CH₂NMe₂)₂-2,6)](ClO₄)}_n (8) upon its reaction with the organometallic heterobimetallic π-tweezer compound {[Ti](μ-σ,π-CCSiMe₃)₂}AgOClO₃ (7) ([Ti] = (η⁵-C₅H₄SiMe₃)₂Ti).The structures of 6a (M = Pd) and 6b (M = Pt) in the solid state are reported. In both complexes the d⁸-configurated transition metal ions palladium(II) and platinum(II) possess a somewhat distorted square-planar coordination sphere. Coordination number 4 at the group-10 metal atoms M is reached by the coordination of two ortho-substituents Me₂NCH₂, the NCN ipso-carbon atom and the bromide ligand. The NC group is para-positioned with respect to M.     

Neue Kupferkomplexe mit Phosphaalkenliganden. Molekülstruktur von [Cu{P(Mes*)C(NMe2)2}2]BF4 (Mes* = 2,4,6‐tBu3C6H2)

New Copper Complexes Containing Phosphaalkene Ligands. Molecular Structure of [Cu{P(Mes*)C(NMe₂)₂}₂]BF₄ (Mes* = 2,4,6‐tBu₃C₆H₂) Reaction of equimolar amounts of the inversely polarized phosphaalkene tBuP=C(NMe₂)₂ ( 1a ) and copper(I) bromide or copper(I) iodide, respectively, affords complexes [Cu₃X₃{μ‐P(tBu)C(NMe₂)₂}₃] ( 2 ) (X =Br) and ( 3 ) (X = I) as the formal result of the cyclotrimerization of a 1:1‐adduct. Treatment of 1a with [Cu(L)Cl] (L = PiPr₃; SbiPr₃) leads to the formation of compounds [CuCl(L){P(tBu)C(NMe₂)₂}] ( 4a ) (L = PiPr₃) and ( 4b ) (L = SbiPr₃), respectively. Reaction of [(MeCN)₄Cu]BF₄ with two equivalents of PhP=C(NMe₂)₂ ( 1b ) yields complex [Cu{P(Ph)C(NMe₂)₂}₂]BF₄ ( 5b ). Similarly, compounds [Cu{P(Aryl)C(NMe₂)₂}₂]BF₄ ( 5c (Aryl = Mes and 5d (Aryl = Mes*)) are obtained from ArylP=C(NMe₂)₂ ( 1c : Aryl = Mes; 1d : Mes*) and [(MeCN)₄Cu]BF₄ in the presence of SbiPr₃. Complexes 2 , 3 , 4a , 4b , and 5b‐5d are characterized by means of elemental analyses and spectroscopy (¹H‐, ¹³C{¹H}‐, ³¹P{¹H}‐NMR). The molecular structure of 5d is determined by X‐ray diffraction analysis.     

Partnering a Three-Coordinate Gallium Cation with a Hydroborate Counter-Ion for the Catalytic Hydrosilylation of CO2

A novel β-diketiminate stabilized gallium hydride, (^DippL)Ga(Ad)H (where ( ^Dipp L)={HC(MeCDippN)₂}, Dipp=2,6-diisopropylphenyl and Ad=1-adamantyl), has been synthesized and shown to undergo insertion of carbon dioxide into the Ga−H bond under mild conditions. In this case, treatment of the resulting κ¹-formate complex with triethylsilane does not lead to regeneration of the hydride precursor. However, when combined with B(C₆F₅)₃, (^DippL)Ga(Ad)H catalyses the reductive hydrosilylation of CO₂. Under stoichiometric conditions, the addition of one equivalent of B(C₆F₅)₃ to (^DippL)Ga(Ad)H leads to the formation of a 3-coordinate cationic gallane complex, partnered with a hydroborate anion, [(^DippL)Ga(Ad)][HB(C₆F₅)₃]. This complex rapidly hydrometallates carbon dioxide and catalyses the selective reduction of CO₂ to the formaldehyde oxidation level at 60 °C in the presence of Et₃SiH (yielding H₂C(OSiEt₃)₂). When catalysis is undertaken in the presence of excess B(C₆F₅)₃, appreciable enhancement of activity is observed, with a corresponding reduction in selectivity: the product distribution includes H₂C(OSiEt₃)₂, CH₄ and O(SiEt₃)₂. While this system represents proof-of-concept in CO₂ hydrosilylation by a gallium hydride system, the TOF values obtained are relatively modest (max. 10 h⁻¹). This is attributed to the strength of binding of the formatoborate anion to the gallium centre in the catalytic intermediate (^DippL)Ga(Ad){OC(H)OB(C₆F₅)₃}, and the correspondingly slow rate of the turnover-limiting hydrosilylation step. In turn, this strength of binding can be related to the relatively high Lewis acidity measured for the [(^DippL)Ga(Ad)]⁺ cation (AN=69.8).     

C(sp3)−H Oxidative Addition and Transfer Hydrogenation Chemistry of a Titanium(II) Synthon: Mimicry of Late‐Metal Type Reactivity

Two‐electron reduction of the Ti^IV compound (^ketguan)(Im^DippN)Ti(OTf)₂ ( 3 ) gives the arene‐masked complex (^ketguan)(η⁶‐Im^DippN)Ti ( 1 ) in excellent yield. Upon standing in solution, 1 converts to a Ti^IV metallacycle ( 4 ) through dehydrogenation of a pendant isopropyl group. Spectroscopic evidence shows this transformation initially proceeds via the oxidative addition of a C(sp³)?H bond and can be reversed upon exposure of 4 to H₂. Interestingly, treatment of 1 with cyclohexene gives cyclohexane and 4 via a titanium‐mediated transfer hydrogenation reaction, a process that can be extended to catalytically hydrogenate other unsaturated hydrocarbons under mild conditions. These results, rare for the early‐metals, suggest 1 possesses chemical characteristics reminiscent of noble, late‐metals.     

Oxidorhenium(V) and Rhenium(III) Complexes with m-Terphenyl Isocyanides

Reactions of the sterically encumbered m-terphenyl isocyanides CNAr^Dipp2 (Dipp = 2,6-diisopropylphenyl) and CNAr^Mes2 (Mes = 2,4,6-trimethylphenyl) with (NBu₄)[ReOCl₄] in CH₂Cl₂ form stable complexes of the composition (NBu₄)[ReOCl₃(CNAr^R)] or [ReOCl₃(CNAr^R)₂] depending on the amount of isocyanide added. In the [ReOCl₃(CNAr^R)₂] complexes, cis coordination of the two isocyanides is observed for CNAr^Mes2, while the sterically more demanding CNAr^DIPP2 ligands are found in trans positions. The rhenium(III) species [ReCl₃(PPh₃)(CNAr^Mes2)₂] was obtained from the reaction of [ReOCl₃(PPh₃)₂] and CNAr^Mes2. The ν(CN) IR frequencies measured for the Re^V complexes appear at higher wavenumbers than for the uncoordinated isocyanides, which suggests a low degree of backdonation into anti-bonding orbitals of these ligands.     

m -Terphenyl derivative of titanium(III): Cp2TiR (Cp=C5H5; R =2,6-(4-MeC6H4)2C6H3)

The title compound, Cp₂TiR (Cp=C₅H₅; R=2,6-(4-MeC₆H₄)₂C₆H₃), 1, was prepared by reaction of RLi with [Cp₂TiCl]₂. Compound 1 was characterized by elemental analysis, EPR, and single crystal X-ray crystallography. The title compound crystallizes in the monoclinic space group C2/c with the following unit cell dimensions: a=11.1466(7) Å, b=16.4429(11) Å, c=13.0786(8) Å; b=106.2040(10)^°;V=2301.9(3) ų. The EPR spectrum of 1 displays two signals, a high field signal at g=1.979 and a lower field signal at g=1.959. Significantly, 1 is a sterically encumbered m-terphenyl-stabilized trivalent titanocene paramagnetic complex and may be a practical one-electron reducing reagent.     

Formation of 5-phenyl-1,2-dithiole-3-thione from molybdenum dithiopropiolato complexes

Molybdenum dithiopropiolato complexes, [(η⁵-C₅R₄R^′)Mo(CO)₂(η²-S₂CCCPh)] (R=H, R^′=Me 1a, R=R^′=H 1b; R=R^′=Me 1c) react with trimethylamine-N-oxide (TMNO · 2H₂O) under mild thermolysis to form 5-phenyl-1,2-dithiole-3-thione (2). The reaction proceeds through the formation of the oxo-complexes, [(η⁵-C₅R₄R^′)Mo(O)(η³-S₂CCCPh)] (R=H, R^′=Me 3a, R=R^′=H 3b; R=R^′=Me 3c). Direct reaction of 3a-c with TMNO · 2H₂O under thermolysis also results in formation of 2.     

N(B(NMe2)2)(Si(NMe2)3)(Ti(NMe2)3), [N(Si(NMe2)3)(Ti(NMe2)2)]2 und N(SiMe3)(Si(NMe2)3)(Ti(NMe2)3) — Synthese und Charakterisierung neuer molekularer Einkomponentenvorläufer für nitridische und carbonitridische Keramiken

N(B(NMe₂)₂)(Si(NMe₂)₃) (Ti(NMe₂)₃), [N(Si(NMe₂)₃)(Ti(NMe₂)₂)]₂ und N(SiMe₃)(Si(NMe₂)₃)(Ti(NMe₂)₃) — Synthesis and Characterization of New Molecular Single-source Precursors for Nitride and Carbonitride Ceramics Synthesis and spectroscopic data of the title compounds are reported. [N(Si(NMe₂)₃)(Ti(NMe₂)₂)]₂ crystallizes in the space group P1 , a = 8.406(7), b = 10.673(8), c = 10.872(6) Å, α = 68.45(4)°, β = 71.72(4)°, γ = 78.11(7)°, 2 877 diffractometer data (F_o ? 2σF_o), R = 0.051. The compound is characterized by a planar four-membered Ti₂N₂-ring with exocyclic tris(dimethylamino)silyl substituents attached to the nitrogen atoms of the ring.