A PGeP pincer-type germylene, Ge(NCHPBu)CH, which contains two phosphane groups hanging from the N atoms of an N-heterocyclic germylene fragment, has been isolated for the first time. This compound has already furnished a rich transition metal derivative chemistry (Co, Rh, and Pd) that includes complexes containing bridging P,Ge,P-, chelating P,Ge- and pincer P,Ge,P-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). Simple chloride exchange reactions led to the methoxidogermyl, methylgermyl, and phenylgermyl derivatives [MCl{κ P,Ge,P-GeR(NCH PtBu ) C H }] (M=Pd, Pt; R=OMe, Me, Ph). Whereas the palladium complexes [PdCl{κ P,Ge,P-GeR(NCH PtBu ) C H }] (R=Me, Ph) reacted with more MeLi or PhLi to give palladium black and GeR (NCH PtBu ) C H (R=Me, Ph), similar reactions with the analogous platinum complexes afforded the transmetalation derivatives [PtR{κ P,Ge,P-GeR(NCH PtBu ) C H }] (R=Me, Ph). The short length of the CH PtBu arms of the PGeP pincer ligands forces the metal atoms of all these complexes to be in a very distorted square-planar ligand environment. The reactivity results have been rationalized with theoretical calculations.

Different coordination modes of a PGeP chloridogermyl ligand (Ge,P-chelating and P,Ge,P-tripodal) and a PGeP germylene ligand (P,Ge,P-bridging and Ge,P-chelating) have been identified in coordination compounds resulting from reactions of the PGeP pincer-type diphosphane-germylene Ge­(NCH2P t Bu2)2C6H4 (1) with iridium­(I), manganese(0), and ruthenium­(II) complex reagents. Germylene 1 reacted with [Ir2(μ-Cl)2(η4-cod)2] (cod = 1,5-cyclooctadiene) to give [Ir­{κ2 Ge,P-GeCl­(NCH2P t Bu2)2C6H4}­(η4-cod)] (2), which contains a Ge,P-chelating PGeP chloridogermyl ligand and an uncoordinated phosphane group that weakly interacts with the Ge atom. Carbon monoxide readily displaced the cod ligand of 2 to give the dicarbonyl derivative [Ir­{κ3 P,Ge,P-GeCl­(NCH2P t Bu2)2C6H4}­(CO)2] (3), in which the PGeP chloridogermyl ligand displays a P,Ge,P-tripodal coordination mode. A bridging germylene moiety has been identified in the binuclear derivative [Mn2{μ-κ3 P,Ge,P-Ge­(NCH2P t Bu2)2C6H4}­(CO)8] (4), which resulted from the treatment of [Mn2(CO)10] with germylene 1. The ruthenium complex [RuHCl­(CO)­{κ2 Ge,P-Ge­(NCH2P t Bu2)2C6H4}­(P i Pr3)] (5), which was isolated from the reaction of 1 with [RuHCl­(CO)­(P i Pr3)2], is the first transition-metal derivative of 1 in which the germylene moiety has not inserted into an M–M or M–Cl bond (M = transition metal), as it contains germylene 1 coordinated in a Ge,P-chelating mode, the resulting GeNCPRu ring being severely strained due to the short length of the coordinated CH2P t Bu2 arm, which also forces the germanium atom to be in an uncommon T-shaped environment. DFT calculations have been used to shed light on bonding features of complexes 2 and 5. The X-ray structures of 1–5 are also reported.

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. The size of the E atom and the strength of stabilizing donor-acceptor PE interactions (both increase on going down in group 14) are key factors in determining the molecular structures of these diphosphanetetrylenes. The syntheses of the chloridostannyl complexes [Rh{κ2Sn,P-SnCl(NCH2PtBu2)2C6H4}(η4-cod)] (5), [RuCl{κ2Sn,P-SnCl(NCH2PtBu2)2C6H4}(η6-cym)] (6) and [IrCl{κ2Sn,P-SnCl(NCH2PtBu2)2C6H4}(η5-C5Me5)] (7) have demonstrated the tendency of stannylene 1 to insert its Sn atom into M-Cl bonds of transition metal complexes and the preference of the resulting PSnP chloridostannyl group to act as a κ2Sn,P-chelating ligand, maintaining an uncoordinated phosphane fragment. X-ray diffraction data (of 6), 31P{1H} NMR data (of 5-7) and DFT calculations (on 6) are consistent with the existence of a weak PSn interaction involving the non-coordinated P atom of complexes 5-7, similar to that found in stannylene 1.

The complexes [M(κ(3)-N,H,H-mapyBH3)(cod)] (M = Rh, Ir; HmapyBH3 = 2-(methylamino)pyridine-borane; cod = 1,5-cyclooctadiene), which contain a novel anionic tripod ligand coordinated to the metal atom through the amido N atom and through two H atoms of the BH3 group, were prepared by treating the corresponding [M2(μ-Cl)2(cod)2] (M = Rh, Ir) precursor with K[mapyBH3]. X-ray diffraction studies and a theoretical Quantum Theory of Atoms in Molecules analysis of their electron density confirmed that the metal atoms of both complexes are in a very distorted trigonal bipyramidal coordination environment, in which two equatorial sites are asymmetrically spanned by the H-B-H fragment. While both 3c-2e BH-M interactions are more κ(1)-H (terminal σ coordination of the B-H bond) than κ(2)-H,B (agostic-type coordination of the B-H bond), one BH-M interaction is more agostic than the other, and this difference is more marked in the iridium complex than in the rhodium one. This asymmetry is not evident in solution, where the cod ligand and the BH3 group of these molecules participate in two concurrent dynamic processes of low activation energies (variable-temperature NMR and density functional theory studies), namely, a rotation of the cod ligand that interchanges its two alkene fragments (through a square pyramidal transition state) and a rotation of the BH3 group about the B-N bond that equilibrates the three B-H bonds (through a square planar transition state). While the cod rotation has similar activation energy in 2 and 3, the barrier to the BH3 group rotation is higher in the iridium complex than in the rhodium one.

Abstract:The borane adduct of the 2-(methylamido)pyridine anion, [

Theoretical electron density (QTAIM) studies in the gas-phase have shown that the attachment of the BH3 group to the metal atom in complexes [Mn( 3 N,H,H-i Pr2bzamBH3)(CO)3] (1) and [Ru( 5 -benzamidine) is symmetric in the latter but asymmetric in the former, and involves two B-H-metal interactions that are intermediate between  1 H (Shimoi type) and  2 H,B (agostic type). The herein reported results, coupled to previous ones on related complexes having a similar tripod  3 N,H,H-borane ligand, show that the bonding similarities and differences within each particular M(-H)2B moiety are not related to the type of metal atom, nor even to its coordination geometry, but mainly to the molecular symmetry.

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