Jose M. Fernandez-Colinas

A family of germyl rhodium complexes derived from the PGeP germylene 2,2’‐bis(di‐isopropylphosphanylmethyl)‐5,5’‐dimethyldipyrromethane‐1,1’‐diylgermanium(II), Ge(pyrmPⁱPr₂)₂CMe₂(1), has been prepared. Germylene1reacted readily with [RhCl(PPh₃)₃] and [RhCl(cod)(PPh₃)] (cod=1,5‐cyclooctadiene) to give, in both cases, the PGeP‐pincer chloridogermyl rhodium(I) derivative [Rh{κ³P,Ge,P‐GeCl(pyrmPⁱPr₂)₂CMe₂}(PPh₃)] (2). Similarly, the reaction of1with [RhCl(cod)(MeCN)] afforded [Rh{κ³P,Ge,P‐GeCl(pyrmPⁱPr₂)₂CMe₂}(MeCN)] (3). The methoxidogermyl and methylgermyl rhodium(I) complexes [Rh{κ³P,Ge,P‐GeR(pyrmPⁱPr₂)₂CMe₂}(PPh₃)] (R=OMe,4; Me,5) were prepared by treating complex2with LiOMe and LiMe, respectively. Complex5readily reacted with CO to give the carbonyl rhodium(I) derivative [Rh{κ³P,Ge,P‐GeR(pyrmPⁱPr₂)₂CMe₂}(CO)] (6), with HCl, HSnPh₃and Ph₂S₂rendering the pentacoordinate methylgermyl rhodium(III) complexes [RhHX{κ³P,Ge,P‐GeMe(pyrmPⁱPr₂)₂CMe₂}] (X=Cl,7; SnPh₃,8) and [Rh(SPh)₂{κ³P,Ge,P‐GeMe(pyrmPⁱPr₂)₂CMe₂}] (9), respectively, and with H₂to give the hexacoordinate derivative [RhH₂{κ³P,Ge,P‐GeMe(pyrmPⁱPr₂)₂CMe₂}(PPh₃)] (10). Complexes3and5are catalyst precursors for the hydroboration of styrene, 4‐vinyltoluene and 4‐vinylfluorobenzene with catecholborane under mild conditions.

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.

The reactivity of the germylene Ge( ^t Bu ₂ bzam)Mes with [Ir ₂ (μ-Cl) ₂ (η ⁴ -cod) ₂ ] and [Ir ₂ Cl ₂ (μ-Cl) ₂ (η ⁵ -Cp*) ₂ ] differs considerably from that previously communicated for the isostructural silylene Si( ^t Bu ₂ bzam)Mes.

The amidinatogermylene-bridged diruthenium(0) complex [Ru₂{μ–κ²Ge,N-Ge(ⁱPr₂bzam)(HMDS)}(CO)₇] (2; ⁱPr₂bzam = N,N′-bis(iso-propyl)benzamidinate; HMDS = N(SiMe₃)₂) reacted at room temperature with ^tBuNC and PMe₃ to give [Ru₂{μ–κ²Ge,N-Ge(ⁱPr₂bzam)(HMDS)}(L)(CO)₆] (L = ^tBuNC, 3; PMe₃, 4), which contain the new ligand in an axial position on the Ru atom that is not attached to the amidinato fragment. At 70 °C, 2 reacted with PPh₃, PMe₃, dppm, and dppe to give the equatorially substituted derivatives [Ru₂{μ–κ²Ge,N-Ge(ⁱPr₂bzam)(HMDS)}(L)(CO)₆] (L = PPh₃, 5; PMe₃, 6) and [Ru₂{μ–κ²Ge,N-Ge(ⁱPr₂bzam)(HMDS)}(μ–κ²P,P′-L₂)(CO)₅] (L₂ = dppm, 7; dppe, 8). HSiEt₃ and HSnPh₃ were oxidatively added to complex 2 at 70 °C, leading to the coordinatively unsaturated products [Ru₂(ER₃)(μ-H){μ–κ²Ge,N-Ge(ⁱPr₂bzam)(HMDS)}(CO)₅] (ER₃ = SiEt₃, 9; SnPh₃, 10), which easily reacted with ^tBuNC and CO to give the saturated derivatives [Ru₂(ER₃)(μ-H){μ–κ²Ge,N-Ge(ⁱPr₂bzam)(HMDS)}(^tBuNC)(CO)₅] (ER₃ = SiEt₃, 11; SnPh₃, 12) and [Ru₂(ER₃)(μ-H){μ–κ²Ge,N-Ge(ⁱPr₂bzam)(HMDS)}(CO)₆] (ER₃ = SiEt₃, 13; SnPh₃, 14), respectively. Compounds 9–14 have their ER₃ group on the Ru atom that is not attached to the amidinato fragment. In contrast, the reaction of 2 with H₂ at 70 °C led to the unsaturated tetranuclear complex [Ru₄(μ-H)₂{μ–κ²Ge,N-Ge(ⁱPr₂bzam)(HMDS)}₂(CO)₁₀] (15), which also reacted with ^tBuNC and CO to give the saturated derivatives [Ru₄(μ-H)₂{μ–κ²Ge,N-Ge(ⁱPr₂bzam)(HMDS)}₂(L)₂(CO)₁₀] (L = ^tBuNC, 16; CO, 17). All tetraruthenium complexes contain an unbridged metal–metal connecting two germylene-bridged diruthenium units. Under CO atmosphere, complex 17 reverted to compound 2. All of the coordinatively unsaturated products (9, 10, and 15) have their unsaturation(s) located on the Ru atom(s) that is(are) attached to the amidinato fragment(s). In the absence of added reagents, the thermolysis of 2 in refluxing toluene led to [Ru₄{μ–κ²Ge,N-Ge(ⁱPr₂bzam)(HMDS)}{μ₃−κGe-Ge(HMDS)}(μ–κ³N,C,N′-ⁱPr₂bzam)(μ-CO)(CO)₈] (18), which contains two new ligands, a triply bridging germylidyne and a bridging benzamidinate, and that results from the condensation of two molecules of 2 and the activation of the Ge–N bond of the benzamidinatogermylene ligand of 2.

Coordinatively unsaturated germylene-bridged diruthenium(0) complexes have been prepared by treating [Ru₃(CO)₁₂] with amidinate germylenes of the type Ge(R¹bzamR²)(HMDS), but only when the amidinate contains just one very bulky R group (^tBu) (not two).

TheC‐alkyl groups of cationic triruthenium cluster complexes of the type [Ru₃(μ‐H)(μ‐κ²N¹,C² ‐L)(CO)₁₀]⁺(HL represents a genericC‐alkyl‐N‐methylpyrazium species) have been deprotonated to give kinetic products that contain unprecedentedC‐alkylidene derivatives and maintain the original edge‐bridged decacarbonyl structure. When the starting complexes contain variousC‐alkyl groups, the selectivity of these deprotonation reactions is related to the atomic charges of the alkyl H atoms, as suggested by DFT/natural‐bond orbital (NBO) calculations. Three additional electronic properties of theC‐alkyl CH bonds have also been found to correlate with the experimental regioselectivity because, in all cases, the deprotonated CH bond has the smallest electron density at the bond critical point, the greatest Laplacian of the electron density at the bond critical point, and the greatest total energy density ratio at the bond critical point (computed by using the quantum theory of atoms in molecules, QTAIM). The kinetic decacarbonyl products evolve, under appropriate reaction conditions that depend upon the position of theC‐alkylidene group in the heterocyclic ring, toward face‐capped nonacarbonyl derivatives (thermodynamic products). The position of theC‐alkylidene group in the heterocyclic ring determines the distribution of single and double bonds within the ligand ring, which strongly affects the stability of the neutral decacarbonyl complexes and the way these ligands coordinate to the metal atoms in the nonacarbonyl products. The mechanisms of these decacarbonylation processes have been investigated by DFT methods, which have rationalized the structures observed for the final products and have shed light on the different kinetic and thermodynamic stabilities of the reaction intermediates, thus explaining the reaction conditions experimentally required by each transformation.

The reactions of [AuCl(THT)] (THT = tetrahydrothiophene) with 1 equiv of the group 14 diaminometalenes M(HMDS)₂ [M = Ge, Sn; HMDS = N(SiMe₃)₂] lead to [Au{MCl(HMDS)₂}(THT)] [M = Ge (1), Sn (2)], which contain a metalate(II) ligand that arises from insertion of the corresponding M(HMDS)₂ reagent into the Au–Cl bond of the gold(I) reagent. While compound 1 reacts with more Ge(HMDS)₂ to give the germanate–germylene derivative [Au{GeCl(HMDS)₂}{Ge(HMDS)₂}] (3), which results from substitution of Ge(HMDS)₂ for the THT ligand of 1, an analogous treatment of compound 2 with Sn(HMDS)₂ gives the stannate–stannylene derivative [Au{SnCl(HMDS)₂}{Sn(HMDS)₂(THT)}] (4), which has a THT ligand attached to the stannylene tin atom and which, in solution at room temperature, participates in a dynamic process that makes its two Sn(HMDS)₂ fragments equivalent (on the NMR time scale). A similar dynamic process has not been observed for the AuGe₂ compound 3 or for the AuSn₂ derivatives [Au{SnR(HMDS)₂}{Sn(HMDS)₂(THT)}] [R = Bu (5), HMDS (6)], which have been prepared by treating complex 4 with LiR. The structures of compounds 1 and 3–6 have been determined by X-ray diffraction.