A Lead-μ-Tetrylide Complex with Osmium(IV) Terminal Components.

A bare lead atom is a σ-donor ligand capable of linearly bonding and stabilizing two units of a classical polyhydride complex, with a high-valent metal center. As a proof of concept, we have prepared and characterized the μ-tetrylide complex (PPr)HOs═Pb═OsH(PPr) in the reaction of OsH(PPr) with Pb{N(SiMe)}. Although the Pb-Os bonds exhibit electrostatic interaction, the main orbital interactions result from two dative σ bonds from the lead atom to the osmium centers.

Attaching Metal-Containing Moieties to β-Lactam Antibiotics: The Case of Penicillin and Cephalosporin.

Procedures for the preparation of transition metal complexes having intact bicyclic cepham or penam systems as ligands have been developed. Starting from readily available 4-azido-2-azetidinones, a synthetic approach has been tuned using a copper-catalyzed azide-alkyne cycloaddition between 3-azido-2-azetinones and alkynes, followed by methylation and transmetalation to Au(I) and Ir(III) complexes from the mesoionic carbene Ag(I) complexes. This methodology was applied to 6-azido penam and 7-azido cepham derivatives to build 6-(1,2,3-triazolyl)penam and 7-(1,2,3-triazolyl)cepham proligands, which upon methylation and metalation with Au(I) and Ir(III) complexes yielded products derived from the coordination of the metal to the penam C and cepham C positions, preserving intact the bicyclic structure of the penicillin and cephalosporin scaffolds.

Polydentate Amidinato-Silylenes, -Germylenes and -Stannylenes.

This review article focuses on amidinatotetrylenes that potentially can (or have already shown to) behave as bi- or tridentate ligands because they contain at least one amidinatotetrylene moiety (silylene, germylene or stannylene) and one (or more) additional coordinable fragment(s). Currently, they are being widely used as ligands in coordination chemistry, small molecule activation and catalysis. This review classifies those that have been isolated as transition metal-free compounds into five families that differ in the position(s) of the donor group(s) (D) on the amidinatotetrylene moiety, namely: ED{RNC(R)NR}, EX{DNC(R)NR}, EX{RNC(D)NR}, EX{DNC(R)ND} and E{RNC(R)ND} (E=Si, Ge or Sn).

A cross-metathesis approach for polymetallic [FeFe]-hydrogenase mimics.

A method has been developed for synthesizing [FeFe]-Hase mimics with diverse structures and properties, employing cross-metathesis of olefins. Vinylmetallocenes (5 and 6) and vinyl half-sandwich complexes (10 and 11) have been used as cross-metathesis partners with [FeFe]-Hase mimics (4, 8, and 9) bearing a double bond in the moiety attached to the ADT-bridge nitrogen. Electrochemical studies of these complexes, encompassing metallocene-type (7a-b, 12a-b, and 13a-b) as well as half-sandwich derivatives (12c and 13c-d), have demonstrated that the introduction of a redox unit has a marginal impact on the reduction potential of these [FeFe]-Hase mimics.

Fast and scalable solvent-free access to Lappert's heavier tetrylenes E{N(SiMe)} (E = Ge, Sn, Pb) and ECl{N(SiMe)} (E = Ge, Sn).

Iconic Lappert's heavier tetrylenes E{N(SiMe)} (E = Ge (1), Sn (2), Pb (3)) have been efficiently prepared from GeCl·(1,4-dioxane), SnCl or PbCl and Li{N(SiMe)} a completely solvent-free one-pot mechanochemical route followed by sublimation. This fast, high-yielding and scalable approach (2 has been prepared in a 100 mmol scale), which involves a small environmental footprint, represents a remarkable improvement over any synthetic route reported over the last five decades, being a so far rare example of the use of mechanochemistry in the realm of main group chemistry. This solventless route has been successfully extended to the preparation of other heavier tetrylenes, such as ECl{N(SiMe)} (E = Ge (4), Sn (5)).

Correction: Fast and scalable solvent-free access to Lappert's heavier tetrylenes E{N(SiMe)} (E = Ge, Sn, Pb) and ECl{N(SiMe)} (E = Ge, Sn).

[This corrects the article DOI: 10.1039/D3SC02709K.].

Synthesis and Some Coordination Chemistry of Phosphane-Difunctionalized Bis(amidinato)-Heavier Tetrylenes: A Previously Unknown Class of PEP Tetrylenes (E = Ge and Sn).

The bis(amidinato)-heavier tetrylenes E(bzamP) (E = Ge () and Sn (); bzamP = -isopropyl-'-(diphenylphosphanylethyl)benzamidinate), which are equipped with one heavier tetrylene (germylene or stannylene) and two phosphane fragments (one on each amidinate moiety) as coordinable groups, have been synthesized from the benzamidinum salt [HbzamP]Cl and GeCl(dioxane) or SnCl in 2:1 mol ratio. A preliminary inspection of their coordination chemistry has shown that their amidinate group can also be involved in the bonding with the metal atoms as tridentate ENP and tetradentate PENP' coordination modes have been observed for the ECl(bzamP) ligand of [Ir{κ,,-ECl(bzamP)}(cod)] (E = Ge () and Sn (); cod = η-1,5-cyclooctadiene) and the E(bzamP) ligand of [Ni{κ,,,'-E(bzamP)}] (E = Ge () and Sn ()), which are products of reactions of and with [IrCl(cod)] (1:0.5 mol ratio) and [Ni(cod)] (1:1 mol ratio), respectively.

Synthesis, Structure, and Photophysical Properties of Platinum(II) (,,') Pincer Complexes Derived from Purine Nucleobases†.

The synthesis of a series of Pt{κ-,,'-[L]}X (X = Cl, RC≡C) pincer complexes derived from purine and purine nucleosides is reported. In these complexes, the 6-phenylpurine skeleton provides the ,-cyclometalated fragment, whereas an amine, imine, or pyridine substituent of the phenyl ring supplies the additional '-coordination point to the pincer complex. The purine ,-fragment has two coordination positions with the metal (1 and 7), but the formation of the platinum complexes is totally regioselective.

Tetrelanes versus Tetrylenes as Precursors to Transition Metal Complexes Featuring Tridentate PEP Tetryl Ligands (E=Si, Ge, Sn).

Two synthetic approaches have until now been used to synthesize transition metal complexes having a tridentate (pincer or tripod) PEP tetryl (E=Si, Ge, Sn) ligand. These approaches differ in the metal-free precursor, tetrelane or tetrylene, that gives rise to the corresponding PEP tetryl ligand. Tetrelanes (PSiP silanes, PGeP germanes and PSnP stannanes and simple phosphane-free stannanes) have led to tetryl ligands by oxidatively adding an E-X bond (X=H, C or halogen in most cases) to the metal atom of a low-valent transition metal complex, whereas tetrylenes (PGeP germylenes and PSnP stannylenes) have led to tetryl ligands upon insertion of their E atom into an M-X bond (X=Cl in most cases) of the metal precursor or through a derivatization of the E atom after the tetrylene fragment is coordinated to the metal.

Dipyrromethane-Based PGeP Pincer Germyl Rhodium Complexes.

A family of germyl rhodium complexes derived from the PGeP germylene 2,2'-bis(di-isopropylphosphanylmethyl)-5,5'-dimethyldipyrromethane-1,1'-diylgermanium(II), Ge(pyrmP Pr ) CMe (1), has been prepared. Germylene 1 reacted readily with [RhCl(PPh ) ] and [RhCl(cod)(PPh )] (cod=1,5-cyclooctadiene) to give, in both cases, the PGeP-pincer chloridogermyl rhodium(I) derivative [Rh{κ P,Ge,P-GeCl(pyrmP Pr ) CMe }(PPh )] (2). Similarly, the reaction of 1 with [RhCl(cod)(MeCN)] afforded [Rh{κ P,Ge,P-GeCl(pyrmP Pr ) CMe }(MeCN)] (3).

Stannylenes based on pyrrole-phosphane and dipyrromethane-diphosphane scaffolds: syntheses and behavior as precursors to PSnP pincer palladium(II), palladium(0) and gold(I) complexes.

2-Ditertbutylphosphanylmethylpyrrole (HpyrmPBu) and 2,2'-bis(diisopropylphosphanylmethyl)-5,5'-dimethyldipyrromethane ((HpyrmPPr)CMe) have been used to synthesize new P-donor-stabilized stannylenes in which the Sn atom is attached to one, SnCl(HpyrmPBu) (1) and Sn{N(SiMe)}(HpyrmPBu) (2), or two pyrrolyl-phosphane scaffolds, Sn(HpyrmPBu) (3), or to a dipyrromethane-diphosphane scaffold, Sn(pyrmPPr)CMe (4). It has been found that stannylenes 3 and 4 are excellent precursors to transition metal complexes containing PSnP pincer-type ligands. Their reactions with chlorido transition metal complexes have afforded [PdCl{κ,,-SnCl(HpyrmPBu)}] (6), [PdCl{κ,,-SnCl(pyrmPPr)CMe}] (7) and [Au{κ,,-SnCl(HpyrmPBu)}] (8), which contain a PSnP pincer-type chloridostannyl ligand.

Alternative Conceptual Approach to the Design of Bifunctional Catalysts: An Osmium Germylene System for the Dehydrogenation of Formic Acid.

The reaction of the hexahydride OsH(PPr) with a P,Ge,P-germylene-diphosphine affords an osmium tetrahydride derivative bearing a Ge,P-chelate, which arises from the hydrogenolysis of a P-C(sp) bond. This Os(IV)-Ge(II) compound is a pioneering example of a bifunctional catalyst based on the coordination of a σ-donor acid, which is active in the dehydrogenation of formic acid to H and CO. The kinetics of the dehydrogenation, the characterization of the resting state of the catalysis, and DFT calculations point out that the hydrogen formation (the fast stage) exclusively occurs on the coordination sphere of the basic metal center, whereas both the metal center and the σ-donor Lewis acid cooperatively participate in the CO release (the rate-determining step).

Reactions of Late First-Row Transition Metal (Fe-Zn) Dichlorides with a PGeP Pincer Germylene.

The reactivity of the PGeP germylene 2,2'-bis(di-isopropylphosphanylmethyl)-5,5'-dimethyldipyrromethane-1,1'-diylgermanium(II), Ge(pyrmPiPr ) CMe , with late first-row transition metal (Fe-Zn) dichlorides has been investigated. All reactions led to PGeP pincer chloridogermyl complexes. The reactions with FeCl and CoCl afforded paramagnetic square planar complexes of formula [MCl{κ P,Ge,P-GeCl(pyrmPiPr ) CMe }] (M=Fe, Co).

A Z-type PGeP pincer germylene ligand in a T-shaped palladium(0) complex.

A dipyrromethane-based germylene decorated with two phosphane groups has been used to prepare an unusual T-shaped palladium(0) containing a PGeP pincer germylene that acts as a Z-type ligand. This compound is a strong reducing reagent, as it has been easily oxidized to germyl-palladium(ii) derivatives with a gold(i) complex, HCl and PhS through processes that involve formal addition of a bond of the oxidant across the Ge-Pd bond.

Phosphane-functionalized heavier tetrylenes: synthesis of silylene- and germylene-decorated phosphanes and their reactions with Group 10 metal complexes.

The stable phosphane-functionalized heavier tetrylenes E(tBu2bzam)pyrmPtBu2 (E = Si (1Si), Ge (1Ge); tBu2bzam = N,N'-ditertbutylbenzamidinate; HpyrmPtBu2 = ditertbutyl(2-pyrrolylmethyl)phosphane) have been prepared by reacting the amidinatotetrylenes E(tBu2bzam)Cl (E = Si, Ge) with LipyrmPtBu2. The reactions of 1Si and 1Ge with selected M0 and MII (M = Ni, Pd, Pt) metal precursors have allowed the synthesis of square-planar [MCl2{κ2E,P-E(tBu2bzam)pyrmPtBu2}] (M = Ni, Pd, Pt; E = Si, Ge), tetrahedral [Ni{κ2E,P-E(tBu2bzam)pyrmPtBu2}(cod)] (E = Si, Ge; cod = 1,5-cyclooctadiene) and triangular [M{κ2E,P-E(tBu2bzam)pyrmPtBu2}(PPh3)] (M = Pd, Pt; E = Si, Ge) complexes, showing that 1Si and 1Ge are excellent Si,P- and Ge,P-chelating ligands that, due to their large steric bulk, are able to stabilize three-coordinate Pd0 and Pt0 complexes.

A dipyrromethane-based diphosphane-germylene as precursor to tetrahedral copper(i) and T-shaped silver(i) and gold(i) PGeP pincer complexes.

A six-membered ring N-heterocyclic germylene flanked by two CHPPr groups, Ge(pyrmPPr)CMe (1; (HpyrmPPr)CMe = 5,5-dimethyl-1,9-bis(di-isopropylphosphanylmethyl)dipyrromethane), has been prepared in high yield. Upon treatment with group 11 metal precursors of the type [MCl(PPh)] (M = Cu (n = 4), Ag (n = 4), Au (n = 1)), germylene 1 easily forms a PGeP chloridogermyl ligand that is able to stabilize tetrahedral copper(i) and unusual T-shaped silver(i) and gold(i) PGeP pincer complexes, as has been demonstrated by the isolation of [Cu{κP,Ge,P-GeCl(pyrmPPr)CMe}(PPh)] (2) and [M{κP,Ge,P-GeCl(pyrmPPr)CMe}] (M = Ag (3), Au (4)). Theoretical calculations have shown that the Ge-M bonds of these complexes are weak and that their strength decreases in the series 2 > 3 > 4.

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 (HpyrmPtBu ), by treating 2-dimethylaminomethylpyrrole (HpyrmNMe ) with tBu PH at 135 °C in the absence of any solvent, has allowed the preparation of the new PGeP germylene Ge(pyrmPtBu ) (1), by treating [GeCl (dioxane)] with LipyrmPtBu , 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{κ P,Ge,P-GeCl(pyrmPtBu ) }] [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{κ P,Ge,P-GeCl(pyrmPtBu ) }] (5), which is a rare case of a T-shaped gold(I) complex.

Mesityl(amidinato)tetrylenes as ligands in iridium(i) and iridium(iii) complexes: silicon versus germanium and simple κ-coordination versus cyclometallation.

Reactions of the mesityl(amidinato)tetrylenes E(Bubzam)Mes (Bubzam = N,N'-bis(tert-butyl)benzamidinate; Mes = mesityl; E = Ge (1), Si (1)) with the iridium precursors [Ir(μ-Cl)(η-cod)] (cod = 1,5-cyclooctadiene) and [IrCl(μ-Cl)(η-Cp*)] (Cp* = 1,2,3,4,5-pentamethylcyclopentadienyl) at room temperature led to simple coordination of the tetrylene in the case of the germylenes ([IrCl(η-cod){κGe-Ge(Bubzam)Mes}] (2) and [IrCl(η-Cp*){κGe-Ge(Bubzam)Mes}] (3), respectively, but to cyclometallated products in the case of the silylenes ([IrHCl(η-cod){κC,Si-Si(Bubzam)CHCHMe}] (4) and [IrCl(η-Cp*){κC,Si-Si(Bubzam)CHCHMe}] (5), respectively. While the cyclometallation of the germylene ligand of the iridium(i) complex 2 could not be achieved by heating this complex in toluene at 90 °C, a similar treatment of the iridium(iii) complex 3 led to [IrCl(η-Cp*){κC,Ge-Ge(Bubzam)CHCHMe}] (5), which is the germanium analogue of 5. DFT calculations have shown that the mononuclear κE-tetrylene iridium(i) complexes [IrCl(η-cod){κE-E(Bubzam)Mes}] (E = Si, Ge; isolated only for E = Ge, 2) should not participate as intermediates in the synthesis of the cyclometallated iridium(iii) derivatives [IrHCl(η-cod){κC,E-E(Bubzam)(CHCHMe)}] (E = Ge, Si; isolated only for E = Si, 4).

Two Types of σ-Allenyl Complexes from Reactions of Silylenes and Germylenes with Chromium Fischer Alkynyl(alkoxy)carbenes.

The reactivity of amidinatotetrylenes of the type E(tBu bzm)R (E=Si, Ge; tBu bzm=N,N'-bis(tertbutyl)benzamidinate; R =alkyl or aryl) with the chromium Fischer alkynylcarbene complexes [Cr{C(OEt)C R }(CO) ] (R =Ph; ferrocenyl, Fc) has been studied. At room temperature, two different reaction pathways have been identified: (a) attack of the amidinatotetrylene to the alkynyl C atom (γ-attack), which leads to σ-allenyl complexes in which the original C atom maintains its attachment to the Cr(CO) and OEt groups (compounds 3 ), and (b) attack of the amidinatotetrylene to the C atom (α-attack), which ends in σ-allenyl complexes in which the original C atom is not attached to the metal atom and has been inserted into an E-N bond of the amidinatotetrylene forming an E-C-N-C-N five-membered ring (compounds 4 ). It has been found that compounds 3 are thermodynamically less stable than their corresponding 4 isomers and that some of the former (E=Ge; R =CH SiMe ) can be transformed into the latter upon heating.

Unexpected Zwitterionic Allenyls from Silylenes and a Fischer Alkynylcarbene: A Remarkable Silylene-Promoted Rearrangement.

The silylenes Si(tBu bzam)R (tBu bzam=N,N'-bis(tertbutyl)benzamidinate; R=mesityl, CH SiMe ) attack the C atom of the Fischer alkynyl(ethoxy)carbene complex [W(CO) {C(OEt)C Ph}] to give, after a striking rearrangement, zwitterionic σ-allenyl complexes in which the original carbene C atom forms part of the allene C fragment and also of a Si-C-N-C-N five-membered ring after insertion into a Si-N bond of the original amidinatosilylene. These remarkable allenyl products, which contain two stereogenic groups, are selectively formed as single diastereomers.

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) {Ge(tBu bzamC(OEt)Me)tBu}] (3 ; M=Cr, W), which occurs readily at room temperature from the germylene Ge(tBu bzam)tBu (1 ) and Fischer carbenes [M(CO) {C(OEt)Me}] (2 ; M=Cr, W), has been found to be reversible. Upon heating at 60 °C, complexes 3 undergo epimerization to an equilibrium mixture of 3 and 3' . At that temperature, the chromium epimers (but not the tungsten ones) release CO to end in the mixed germylene-Fischer carbene complexes [Cr(CO) {C(OEt)Me}{Ge(tBu bzam)tBu}] (cis-4 and trans-4 ).

Synthesis and some coordination chemistry of the PSnP pincer-type stannylene Sn(NCHPBu)CH, attempts to prepare the PSiP analogue, and the effect of the E atom on the molecular structures of E(NCHPBu)CH (E = C, Si, Ge, Sn).

The non-donor-stabilized PSnP pincer-type stannylene Sn(NCH2PtBu2)2C6H4 (1) has been prepared by treating SnCl2 with Li2(NCH2PtBu2)2C6H4. All attempts to synthesize the analogous PSiP silylene by reduction of the (previously unknown) silanes SiCl2(NCH2PtBu2)2C6H4 (2), SiHCl(NCH2PtBu2)2C6H4 (3) and SiH(HMDS)(NCH2PtBu2)2C6H4 (4; HMDS = N(SiMe3)2) have been unsuccessful. The almost planar (excluding the tert-butyl groups) molecular structure of stannylene 1 (determined by X-ray crystallography) has been rationalized with the help of DFT calculations, which have shown that, in the series of diphosphanetetrylenes E(NCH2PtBu2)2C6H4 (E = C, Si, Ge, Sn), the most stable conformation of the compounds with E = Ge and Sn has both P atoms very close to the EN2C6H4 plane, near (interacting with) the E atom, whereas for the compounds with E = C and Si, both phosphane groups are located at one side of the EN2C6H4 plane and far away from the E atom.

Facile cyclometallation of a mesitylsilylene: synthesis and preliminary catalytic activity of iridium(iii) and iridium(v) iridasilacyclopentenes.

Reactions of the mesityl-amidinato-silylene Si(Bubzam)Mes (1; Bubzam = N,N'-bis(tert-butyl)benzamidinato; Mes = mesityl) with three different iridium precursors led, at room temperature, to two iridium(iii) and one iridium(v) complexes featuring one (Ir) or two (Ir) cyclometallated silylene ligands. The iridium(iii) complexes are active catalyst precursors for H/D exchange and dehydrogenative borylation of arene C-H bonds.

From a Diphosphanegermylene to Nickel, Palladium, and Platinum Complexes Containing Germyl PGeP Pincer Ligands.

The PGeP pincer-type germylene Ge(NCH PtBu )C H (1) has been used to prepare a family of group 10 metal complexes, namely, [MCl{κ P,Ge,P-GeCl(NCH PtBu ) C H }] (M=Ni (2 ), Pd (2 ), Pt (2 )), featuring a chloridogermyl PGeP pincer ligand and a Cl-Ge-M-Cl bond sequence. Their reactivity is not initially centered on the metal atom but on their Ge atom. Complexes 2 and 2 easily led to the hydrolyzed products [Ni Cl {μ-(κ P,Ge,P-Ge(NCH PtBu ) C H ) O}], which features a Cl-Ni-Ge-O-Ge-Ni-Cl bond sequence, and [PdCl{κ P,Ge,P-Ge(OH)(NCH PtBu ) C H }], which contains a hydroxidogermyl PGeP pincer ligand (2 is reluctant to undergo hydrolysis).