Reversible Carbene Insertion into a Ge−N Bond and Insights into CO and Carbene Substitution Reactions Involving Amidinatogermylenes and Fischer Carbene Complexes

The formation of the five-membered-ring germylene complexes [M(CO)₅{Ge(tBu₂bzamC(OEt)Me)tBu}] ( 3_M ; M=Cr, W), which occurs readily at room temperature from the germylene Ge(tBu₂bzam)tBu ( 1 _{t Bu} ) and Fischer carbenes [M(CO)₅{C(OEt)Me}] ( 2_M ; M=Cr, W), has been found to be reversible. Upon heating at 60 °C, complexes 3_M undergo epimerization to an equilibrium mixture of 3_M and 3′_M . At that temperature, the chromium epimers (but not the tungsten ones) release CO to end in the mixed germylene–Fischer carbene complexes [Cr(CO)₄{C(OEt)Me}{Ge(tBu₂bzam)tBu}] (cis- 4_Cr and trans- 4_Cr ). The latter decompose at 120 °C to [Cr(CO)₅{Ge(tBu₂bzam)tBu}] ( 6_Cr ). Because the formation of cis- 4_Cr and trans- 4_Cr from 3_Cr or 3′_Cr requires the presence of free 1 _{t Bu} and 2_Cr in the reaction solutions, the reactions of 1 _{t Bu} with 2_M to give 3_M (and 3′_M at 60 °C) should be reversible. This proposal has been proven by germylene-exchange crossover reactions in which free 1 _{t Bu} and [M(CO)₅{Ge(tBu₂bzamC(OEt)Me)CH₂SiMe₃}] ( 5′_M ; M=Cr, W) were formed when complexes 3_M were treated at room temperature with the germylene Ge(tBu₂bzam)CH₂SiMe₃ ( 1_tmsm ). A clear differential behavior between N-heterocyclic carbenes (NHCs) and amidinatogermylenes ( 1 _{t Bu} and 1_tmsm ) in their reactivity against group 6 metal Fischer carbene complexes is demonstrated. The higher electron-donor capacity of amidinatogermylenes with respect to NHCs and the bias of the former to get involved in ring expansion processes are responsible for this differential behavior.     

Bond Formation and Coupling between Germyl and Bridging Germylene Ligands in Dinuclear Palladium(I) Complexes

The dinuclear palladium(I) complexes [L(Ar₂HGe)Pd(μ‐GeAr₂)₂Pd(GeHAr₂)L] (Ar=Ph, p‐Tol; L=PMe₃, tBuNC) contain terminal germyl and bridging germylene ligands with the experimentally observed Ge???Ge bond lengths of 2.8263(4) Å (L=PMe₃) and 2.928(1) Å (L=tBuNC), which are close to the longest Ge? Ge bond reported to date [2.714(1) Å]. Significant Ge???Ge interactions between the germylene and germyl ligands (PMe₃ complexes > tBuNC complexes) are supported by DFT calculations, Wiberg bond indices (WBI), and natural bond orbital (NBO) analyses. Exchanging tBuNC for PMe₃ ligands increases the Ge???Ge interaction, and simultaneously activates two Pd? Ge bonds. Adding the chelating diphosphine 1,2‐bis(diethylphosphino)ethane (depe) to the PMe₃ complexes results in the intramolecular coupling of germyl and germylene ligands followed by extrusion of a digermane.     

The “Metallo”-Diels–Alder Reactions: Examining the Metalloid Behavior of Germanimines

Addition of MesN₃ (Mes=2,4,6-Me₃C₆H₂) to germylene [(NON^tBu)Ge] (NON^tBu=O(SiMe₂NtBu)₂) ( 1 ) gives germanimine, [(NON^tBu)Ge=NMes] ( 2 ). Compound 2 behaves as a metalloid, showing reactivity reminiscent of both transition metal-imido complexes, undergoing [2+2] addition with heterocumulenes and protic sources, as well as an activated diene, undergoing a [4+2] cycloaddition, or “metallo”-Diels–Alder, reaction. In the latter case, the diene includes the Ge=N bond and π-system of the Mes substituent, which is reactive towards dienophiles including benzaldehyde, benzophenone, styrene, and phenylacetylene.     

An Amidinate‐Stabilized Germatrisilacyclobutadiene Ylide

The synthesis and characterization of new amidinate‐stabilized germatrisilacyclobutadiene ylides [L₃Si₃GeL′] (L=PhC(NtBu)₂; L′=ËL; Ë=Ge ( 3 ), Si ( 7 )) are described. Compound 3 was prepared by the reaction of [LSi? SiL] ( 1 ) with one equivalent of [LGe? GeL] ( 2 ) in THF. Compound 7 was synthesized by the reaction of 2 with excess 1 in THF. The bisamidinate germylene [L₂Ge:] ( 4 ) is a by‐product in both reactions. Moreover, compound 7 was prepared by the reaction of 3 with one equivalent of 1 in THF. Compounds 3 and 7 have been characterized by NMR spectroscopy, X‐ray crystallography, and theoretical studies. The results show that compounds 3 and 7 are not antiaromatic. The puckered Si₃Ge four‐membered rings in 3 and 7 have a ylide structure, which is stabilized by amidinate ligands and the electron delocalization within the Si₃Ge four‐membered ring.     

Diverse Reactivity of bis(Silylene) and bis(Germylene) [LE−EL (E=Si and Ge: L=PhC(NtBu)2)] in the Oxidative Activation of C−F Bond: Si−Si Bond is Retained While the Ge−Ge Bond Is Cleaved

Herein we report the reactions of 3,4,5,6-tetrafluoroterephthalonitrile ( 1 ) with bis(silylene) and bis(germylene) LE−EL [E=Si ( 2 ) and Ge( 3 ): L=PhC(N^tBu)₂)]. The reaction of LSi−SiL (L=PhC(N^tBu)₂) ( 2 ) with two equivalents of 1 resulted in an unprecedented oxidative addition of a C−F bond of 1 leading to disilicon(III) fluoride {L(4-C₈F₃N)FSi−SiF(4-C₈F₃N)L}( 4 ), wherein the Si−Si single bond was retained. In contrast, the reaction of LGe−GeL (L=PhC(N^tBu)₂) ( 3 ) with one equivalent of 1 resulted in the oxidative cleavage of Ge−Ge bond leading to L(4-C₈F₃N₂)Ge ( 5 ) and LGeF ( 6 ). All three compounds ( 4 – 6 ) were characterized by NMR spectroscopy, EI-MS spectrometry, and elemental analysis. X-ray single-crystal structure determination of compound 4 unequivocally established that the Si^III−Si^III bond remains uncleaved.     

Ring Opening and Bidentate Coordination of Amidinate Germylenes and Silylenes on Carbonyl Dicobalt Complexes: The Importance of a Slight Difference in Ligand Volume

The reactions of [Co₂(CO)₈] with one equiv of the benzamidinate (R₂bzam) group‐14 tetrylenes [M(R₂bzam)(HMDS)] (HMDS=N(SiMe₃)₂; 1 : M=Ge, R=iPr; 2 : M=Si, R=tBu; 3 : M=Ge, R=tBu) at 20 °C led to the monosubstituted complexes [Co₂{κ¹M?M(R₂bzam)(HMDS)}(CO)₇] ( 4 : M=Ge, R=iPr; 5 : M=Si, R=tBu; 6 : M=Ge, R=tBu), which contain a terminal κ¹M–tetrylene ligand. Whereas the Co₂Si and Co₂Ge tert‐butyl derivatives 5 and 6 are stable at 20 °C, the Co₂Ge isopropyl derivative 4 evolved to the ligand‐bridged derivative [Co₂{μ‐κ²Ge,N‐Ge(iPr₂bzam)(HMDS)}(μ‐CO)(CO)₅] ( 7 ), in which the Ge atom spans the Co?Co bond and one arm of the amidinate fragment is attached to a Co atom. The mechanism of this reaction has been modeled with the help of DFT calculations, which have also demonstrated that the transformation of amidinate‐tetrylene ligands on the dicobalt framework is negligibly influenced by the nature of the group‐14 metal atom (Si or Ge) but is strongly dependent upon the volume of the amidinate N?R groups. The disubstituted derivatives [Co₂{κ¹M?M(R₂bzam)(HMDS)}₂(CO)₆] ( 8 : M=Ge, R=iPr; 9 : M=Si, R=tBu; 10 : M=Ge, R=tBu), which contain two terminal κ¹M–tetrylene ligands, have been prepared by treating [Co₂(CO)₈] with two equiv of 1 – 3 at 20 °C. The IR spectra of 8 – 10 have shown that the basicity of germylenes 1 and 3 is very high (comparable to that of trialkylphosphanes and 1,3‐diarylimidazol‐2‐ylidenes), whereas that of silylene 2 is even higher.     

8‐Amidoquinoline, 8‐(Trialkylsilylamido)quinoline, 2‐Pyridylmethylamide,and (2‐Pyridylmethyl)(trialkylsilyl)amide Complexes of Gallium

Lithium 8‐amidoquinoline ( 1 ) and lithium 8‐(trialkylsilylamido)quinoline [SiMe₂tBu ( 2 ), SiiPr₃ ( 3 )] react with dimethylgallium chloride to the metathesis products dimethylgallium 8‐amidoquinoline ( 4 ) as well as dimethylgallium 8‐(trialkylsilylamido)quinoline [SiMe₂tBu ( 5 ), SiiPr₃ ( 6 )]. The gallium atoms are in distorted tetrahedral environments. During the synthesis of 5 , orange dimethylgallium 2‐butyl‐8‐(tert‐butyldimethylsilylamido)quinoline ( 7 ) was found as by‐product. The metathesis reactions of Me₂GaCl with LiN(R)CH₂Py (Py = 2‐pyridyl) yield the corresponding 2‐pyridylmethylamides Me₂Ga‐N(H)CH₂Py ( 8 ), Me₂Ga‐N(SiMe₂tBu)CH₂Py ( 9 ) and Me₂Ga‐N(SiiPr₃)CH₂Py ( 10 ). In these complexes the gallium atoms show a distorted tetrahedral coordination sphere. However, derivative 8 crystallizes dimeric with bridging amido units whereas in 9 and 10 the 2‐pyridylmethylamido moieties act as bidentate ligands leading to monomeric molecules.     

Investigations of the Nature of ZnII−SiII Bonds

A series of zinc(II) silylenes was prepared by using the silylene {PhC(NtBu)₂}(C₅Me₅)Si. Whereas reaction of the silylene with ZnX₂ (X=Cl, I) gave the halide‐bridged dimers [{PhC(NtBu)₂}(C₅Me₅)SiZnX(μ‐X)]₂, with ZnR₂ (R=Ph, Et, C₆F₅) as reagent the monomers [{PhC(NtBu)₂}(C₅Me₅)SiZnR₂] were obtained. The stability of the complexes and the Zn?Si bond lengths clearly depend on the substitution pattern of the zinc atom. Electron‐withdrawing groups stabilize these adducts, whereas electron‐donating groups destabilize them. This could be rationalized by quantum chemical calculations. Two different bonding modes in these molecules were identified, which are responsible for the differences in reactivity: 1) strong polar Zn?Si single bonds with short Zn?Si distances, Zn?Si force constants close to that of a classical single bond, and strong binding energy (ca. 2.39 Å, 1.33 mdyn Å^?1, and 200 kJ mol^?1), which suggest an ion pair consisting of a silyl cation with a Zn?Si single bond; 2) relatively weak donor–acceptor Zn?Si bonds with long Zn?Si distances, low Zn?Si force constants, and weak binding energy (ca. 2.49 Å, 0.89 mdyn Å^?1, and 115 kJ mol^?1), which can be interpreted as a silylene–zinc adduct.     

An N‐Heterocyclic Silylene‐Stabilized Digermanium(0) Complex

The synthesis of an N‐heterocyclic silylene‐stabilized digermanium(0) complex is described. The reaction of the amidinate‐stabilized silicon(II) amide [LSiN(SiMe₃)₂] ( 1 ; L=PhC(NtBu)₂) with GeCl₂?dioxane in toluene afforded the Si^II–Ge^II adduct [L{(Me₃Si)₂N}Si→GeCl₂] ( 2 ). Reaction of the adduct with two equivalents of KC₈ in toluene at room temperature afforded the N‐heterocyclic carbene silylene‐stabilized digermanium(0) complex [L{(Me₃Si)₂N}Si→ Ge?Ge←Si{N(SiMe₃)₂}L] ( 3 ). X‐ray crystallography and theoretical studies show conclusively that the N‐heterocyclic silylenes stabilize the singlet digermanium(0) moiety by a weak synergic donor–acceptor interaction.     

Potential Precursors for Terminal Methylidene Rare-Earth-Metal Complexes Supported by a Superbulky Tris(pyrazolyl)borato Ligand

A series of solvent-free heteroleptic terminal rare-earth-metal alkyl complexes stabilized by a superbulky tris(pyrazolyl)borato ligand with the general formula [Tp^tBu,MeLnMeR] have been synthesized and fully characterized. Treatment of the heterobimetallic mixed methyl/tetramethylaluminate compounds [Tp^tBu,MeLnMe(AlMe₄)] (Ln=Y, Lu) with two equivalents of the mild halogenido transfer reagents SiMe₃X (X=Cl, I) gave [Tp^tBu,MeLnX₂] in high yields. The addition of only one equivalent of SiMe₃Cl to [Tp^tBu,MeLuMe(AlMe₄)] selectively afforded the desired mixed methyl/chloride complex [Tp^tBu,MeLuMeCl]. Further reactivity studies of [Tp^tBu,MeLuMeCl] with LiR or KR (R=CH₂Ph, CH₂SiMe₃) through salt metathesis led to the monomeric mixed-alkyl derivatives [Tp^tBu,MeLuMe(CH₂SiMe₃)] and [Tp^tBu,MeLuMe(CH₂Ph)], respectively, in good yields. The SiMe₄ elimination protocols were also applicable when using SiMe₃X featuring more weakly coordinating moieties (here X=OTf, NTf₂). X-ray structure analyses of this diverse set of new [Tp^tBu,MeLnMeR/X] compounds were performed to reveal any electronic and steric effects of the varying monoanionic ligands R and X, including exact cone-angle calculations of the tridentate tris(pyrazolyl)borato ligand. Deeper insights into the reactivity of these potential precursors for terminal alkylidene rare-earth-metal complexes were gained through NMR spectroscopic studies.     

From a Phosphaketenyl‐Functionalized Germylene to 1,3‐Digerma‐2,4‐diphosphacyclobutadiene

The first 4π‐electron resonance‐stabilized 1,3‐digerma‐2,4‐diphosphacyclobutadiene [L^H₂Ge₂P₂] 4 (L^H=CH[CHNDipp]₂ Dipp=2,6‐ⁱPr₂C₆H₃) with four‐coordinate germanium supported by a β‐diketiminate ligand and two‐coordinate phosphorus atoms has been synthesized from the unprecedented phosphaketenyl‐functionalized N‐heterocyclic germylene [L^HGe‐P=C=O] 2 a prepared by salt‐metathesis reaction of sodium phosphaethynolate (P≡C?ONa) with the corresponding chlorogermylene [L^HGeCl] 1 a . Under UV/Vis light irradiation at ambient temperature, release of CO from the P=C=O group of 2 a leads to the elusive germanium–phosphorus triply bonded species [L^HGe≡P] 3 a , which dimerizes spontaneously to yield black crystals of 4 as isolable product in 67 % yield. Notably, release of CO from the bulkier substituted [L^tBuGe‐P=C=O] 2 b (L^tBu=CH[C(^tBu)N‐Dipp]₂) furnishes, under concomitant extrusion of the diimine [Dipp‐NC(^tBu)]₂, the bis‐N,P‐heterocyclic germylene [DippNC(^tBu)C(H)PGe]₂ 5 .     

Polyimido Sulfur(VI) Phosphanyl Ligand in Metal Complexation

Herein, new complexes containing the [Ph₂PCH₂S(NtBu)₃]^? anion are presented, supplying three imido nitrogen atoms and a remote phosphorus atom as potential donor sites to main group and transition‐metal cations. The lithiated complex [(tmeda)Li{(NtBu)₃SCH₂PPh₂}] ( 1 ) is an excellent starting material in transmetalation reactions. Herein, the transition‐metal complexes [M{(NtBu)₃SCH₂PPh₂}₂] (M=Mn ( 2 ), Ni ( 3 ), Zn ( 4 )) were synthesized and structurally characterized. Their isotypical molecules show SN₂ chelation and no employment of the adjacent phosphorus atom in coordination. The third pendent imido group is always twisted toward the vacant face of the tetrahedrally coordinated sulfur atom.     

Synthesis and characterizations of bis(phenoxy)‐amine tin(II) complexes for ring‐opening polymerization of lactide

A series of tin(II) complexes supported by N₂O₂ bis(phenol)‐amine ligands were prepared from the reactions of the corresponding ligands with Sn[N(SiMe₃)₂]₂ in benzene at room temperature. The ligands were designed to have different substituted group at the ortho‐position on the aryl rings (R = ^tBu, CH₃) and N‐containing side arm (E = ? CH₂NEt₂ and pyridine) giving a variation of tin(II) complexes (R = ^tBu, E = CH₂NEt₂, 2a ; R = ^tBu, E = py, 2b ; R = CH₃, E = CH₂NEt₂, 2c ; R = CH₃, E = py, 2d ). All complexes were characterized by NMR spectroscopy and single‐crystal X‐ray analysis. The single‐crystal X‐ray crystallography revealed that all complexes have a monomeric four‐coordinate tin center with a distorted seesaw structure. All complexes are active for solvent‐free polymerization of l ‐lactide at 120 °C giving poly(l ‐lactide) with narrow to moderate dispersity (Ð = 1.12–1.56). In the presence of benzyl alcohol during the polymerization, the resulting polymer was found to be linear having benzyl alcohol as the end group while, in the absence of benzyl alcohol, the polymer was cyclic. The large ^tBu group at the ortho‐position was found to decrease polymerization activity while the more basic ? CH₂NEt₂ group was found to increase the polymerization activity. The polymerization of rac‐lactide under a similar condition gave PLA having a slight heterotactic bias for all catalysts. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 2104–2112     

Synthesis and Structural Characterization of Some Novel Trialkylsilyl‐substituted Lithium Benzyl Complexes [Li(tmeda)][CHRSiMe2R′] (R = Ph, 3,5‐Me2C6H3; R′ = Me,tBu, Ph)

The reactions of PhCH₂SiMe₃ ( 1 ), PhCH₂SiMe₂^tBu ( 2 ), PhCH₂SiMe₂Ph ( 3 ), 3,5‐Me₂C₆H₃CH₂SiMe₃ ( 4 ), and 3,5‐Me₂C₆H₃CH₂SiMe₂^tBu ( 5 ) with ⁿBuLi in tetramethylethylenediamine (tmeda) afford the corresponding lithium complexes [Li(tmeda)][CHRSiMe₂R′] (R, R′ = Ph, Me ( 6 ), Ph, ^tBu ( 7 ), Ph, Ph ( 8 ), 3,5‐Me₂C₆H₃, Me ( 9 ), and 3,5‐Me₂C₆H₃, ^tBu ( 10 )), respectively. The new compounds 5 , 7 , 8 , 9 and 10 have been characterized by ¹H and ¹³C NMR spectroscopy, compounds 7 , 8 and 9 also by X‐ray structure analysis.     

Pseudohalogenogermylenes versus Halogenogermylenes: Difference in their Complexation Behavior towards Group 6 Metal Carbonyls

Pseudohalogenogermylenes [(iBu)₂ATI]GeY (Y=NCO 4 , NCS 5 ) show different coordination behavior towards group 6 metal carbonyls in comparison to the corresponding halogenogermylenes [(iBu)₂ATI]GeX (X=F 1 , Cl 2 , Br 3 ) (ATI=aminotroponiminate). The reactions of compounds 4 – 5 and 1 – 3 with cis‐[M(CO)₄(COD)] (M=Mo, W, COD=cyclooctadiene) gave trans‐germylene metal complexes {[(iBu)₂ATI]GeY}₂M(CO)₄ (Y=NCO, M=Mo 6 , W 11 ; Y=NCS, M=Mo 7 ) and cis‐germylene metal complexes {[(iBu)₂ATI]GeX}₂M(CO)₄ (M=Mo, X=F 8 , Cl 9 , Br 10 ; M=W, X=Cl 12 ), respectively. Theoretical studies on compounds 7 and 9 reveal that donor–acceptor interactions from Mo to Ge atoms are better stabilized in the observed trans and cis geometries than in the hypothetical cis and trans structures, respectively.     

Phosphine (oxide)‐(thio) phenolate palladium complexes: Synthesis,characterization and (co)polymerization of norbornene

A series of palladium complexes ( 2a–2g ) ( 2a : [6‐^tBu‐2‐PPh₂‐C₆H₃O]PdMe(Py); 2b : [6‐C₆F₅–2‐PPh₂‐C₆H₃O]PdMe(Py); 2c : [6‐^tBu‐2‐PPh^tBu‐C₆H₃O]PdMe(Py); 2d : [2‐PPh^tBu‐C₆H₄O] PdMe(Py); 2e : [6‐SiMe₃–2‐PPh₂‐C₆H₃O]PdMe(Py); 2f : [2‐^tBu‐6‐(Ph₂P=O)‐C₆H₃O]PdMe(Py); 2g : [6‐SiMe₃–2‐(Ph₂P=O)‐C₆H₃S]PdMe(Py)) bearing phosphine (oxide)‐(thio) phenolate ligand have been efficiently synthesized and characterized. The solid‐state structures of complexes 2d , 2f and 2g have been further confirmed by single‐crystal X‐ray diffraction, which revealed a square‐planar geometry of palladium center. In the presence of B(C₆F₅)₃, these complexes can be used as catalysts to polymerize norbornene (NB) with relatively high yields, producing vinyl‐addition polymers. Interestingly, 2a /B(C₆F₅)₃ system catalyzed the polymerization of NB in living polymerization manner at high temperature (polydispersity index 1.07, M_n up to 1.5 × 10⁴). The co‐polymerization of NB and polar monomers was also studied using catalysts 2a and 2f . All the obtained co‐polymers could dissolve in common solvent.     

A Germylene Supported by Two 2-Pyrrolylphosphane Groups as Precursor to PGeP Pincer Square-Planar Group 10 Metal(II) and T-Shaped Gold(I) Complexes

An efficient synthesis of 2-di-tert-butylphosphanylmethylpyrrole (HpyrmPtBu₂), by treating 2-dimethylaminomethylpyrrole (HpyrmNMe₂) with tBu₂PH at 135 °C in the absence of any solvent, has allowed the preparation of the new PGeP germylene Ge(pyrmPtBu₂)₂ ( 1 ), by treating [GeCl₂(dioxane)] with LipyrmPtBu₂, in which the Ge atom is stabilized by intramolecular interactions with one (solid state) or both (solution) of its phosphane groups. Reactions of germylene 1 with Group 10 metal dichlorido complexes containing easily displaceable ligands have led to [MCl{κ³P,Ge,P-GeCl(pyrmPtBu₂)₂}] [M=Ni ( 2 ), Pd ( 3 ), Pt ( 4 )], which have an unflawed square-planar metal environment. Treatment of germylene 1 with [AuCl(tht)] (tht=tetrahydrothiophene) rendered [Au{κ³P,Ge,P-GeCl(pyrmPtBu₂)₂}] ( 5 ), which is a rare case of a T-shaped gold(I) complex. The hydrolysis of 5 gave the linear gold(I) derivative [Au(κP-HpyrmPtBu₂)₂]Cl ( 6 ). Complexes 2 – 5 contain a PGeP pincer chloridogermyl ligand that arises from the insertion of the Ge atom of germylene 1 into a M−Cl bond of the corresponding metal reagent. The bonding in these molecules has been studied by DFT/NBO/QTAIM calculations. These results demonstrate that the great flexibility of germylene 1 makes it a better precursor to PGeP pincer complexes than the previously known germylenes of this type.     

Structural Analysis of Zincocenes with Substituted Cyclopentadienyl Rings

New zincocenes [ZnCp′₂] ( 2 – 5 ) with substituted cyclopentadienyl ligands C₅Me₄H, C₅Me₄tBu, C₅Me₄SiMe₂tBu and C₅Me₄SiMe₃, respectively, have been prepared by the reaction of ZnCl₂ with the appropriate Cp′‐transfer reagent. For a comparative structural study, the known [Zn(C₅H₄SiMe₃)₂] ( 1 ), has also been investigated, along with the mixed‐ring zincocenes [Zn(C₅Me₅)(C₅Me₄SiMe₃)] ( 6 ) and [Zn(C₅Me₅)(C₅H₄SiMe₃)] ( 7 ), the last two obtained by conproportionation of [Zn(C₅Me₅)₂] with 5 or 1 , as appropriate. All new compounds were characterised by NMR spectroscopy, and by X‐ray methods, with the exception of 7 , which yields a side‐product ( C ) upon attempted crystallisation. Compounds 5 and 6 were also investigated by ¹³C CPMAS NMR spectroscopy. Zincocenes 1 and 2 have infinite chain structures with bridging Cp′ ligands, while 3 and 4 exhibit slipped‐sandwich geometries. Compounds 5 and 6 have rigid, η⁵/η¹(σ) structures, in which the monohapto C₅Me₄SiMe₃ ligand is bound to zinc through the silyl‐bearing carbon atom, forming a Zn? C bond of comparable strength to the Zn? Me bond in ZnMe₂. Zincocene 5 has dynamic behaviour in solution, but a rigid η⁵/η¹(σ) structure in the solid state, as revealed by ¹³C CPMAS NMR studies, whereas for 6 the different nature of the Cp′ ligands and of the ring substituents of the η¹‐Cp′ group (Me and SiMe₃) have permitted observation for the first time of the rigid η⁵/η¹ solution structure. Iminoacyl compounds of composition [Zn(η⁵‐C₅Me₄R)(η¹‐C(NXyl)C₅Me₄R)] resulting from the reactions of some of the above zincocenes and CNXyl (Xyl=2,6‐dimethylphenylisocyanide) have also been obtained and characterised.     

New Ga/N‐based Active Lewis Pairs,Trifunctional Ga–Ga Compounds,Reactions with Cyanamide and Dual Insertion of Isocyanate

Hydrogallation of Me₃Si–C≡C–NR'₂ with R₂Ga–H (R = tBu, CH₂tBu, iBu) yielded Ga/N‐based active Lewis pairs, R₂Ga–C(SiMe₃)=C(H)–NR'₂ ( 7 ). The Ga and N atoms adopt cis‐positions at the C=C bonds and show weak Ga–N interactions. tBu₂GaH and Me₃Si–C≡C–N(C₂H₄)₂NMe afforded under exposure of daylight the trifunctional digallium(II) compound [MeN(C₂H₄)₂N](H)C=C(SiMe₃)Ga(tBu)–Ga(tBu)C(SiMe₃)=C(H)[N(C₂H₄)₂NMe] ( 8 ), which results from elimination of isobutene and H₂ and Ga–Ga bond formation. 8 was selectively obtained from the ynamine and [tBu(H)Ga–Ga(H)tBu]₂[HGatBu₂]₂. 7a (R = tBu; NR'₂ = 2,6‐Me₂NC₅H₈) and H₈C₄N–C≡N afforded the adduct tBu₂Ga‐C(SiMe₃)=C(H)(2,6‐Me₂NC₅H₈) · N≡C–NC₄H₈ ( 11 ) with the nitrile bound to gallium. The analogous ALP with harder Al atoms yielded an adduct of the nitrile dimer or oligomers of the nitrile at room temperature. The reaction of 7a with Ph–N=C=O led to the insertion of two NCO groups into the Ga–C_vinyl bond to yield a GaOCNCN heterocycle with Ga bound to O and N atoms ( 12 ).     

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.