Magic-sized nanoclusters have been implicated as mechanistically relevant intermediates in the synthesis of group III-V quantum dots. Herein we report the single-crystal X-ray diffraction structure of a carboxylate-ligated indium phosphide magic-sized nanocluster at 0.83 Å resolution. The structure of this cluster, In37P20(O2CR)51, deviates from that of known crystal phases and possesses a non-stoichiometric, charged core composed of a series of fused 6-membered rings. The cluster is completely passivated by bidentate carboxylate ligands exhibiting predominantly bridging binding modes. The absorption spectrum of the cluster shows an asymmetric line shape that is broader than what would be expected from a homogeneous sample. A combination of computational and experimental evidence suggests that the spectral line width is a result of multiple, discrete electronic transitions that couple to vibrations of the nanocrystal lattice. The product of reaction of this nanocluster with 1 equiv of water has also been structurally characterized, demonstrating site selectivity without a drastic alteration of electronic structure.

Palladium complexes of the novel unsymmetrical phosphine pyrazole-containing pincer ligands PCN H (PCN H = 1-[3-[(di-tert-butylphosphino)methyl]phenyl]-1H-pyrazole) and PCN Me (PCN Me = 1-[3-[(di-tert-butylphosphino)methyl]phenyl]-5-methyl-1H-pyrazole) have been prepared and characterized through single-crystal X-ray diffraction and multinuclear 1 H, 13 C{ 1 H}, and 31 P{ 1 H} NMR spectroscopy. In preparations of the monomeric hydroxide species (PCN H )Pd(OH), an unexpected N detachment followed by C−H activation on the heterocycle 5-position took place resulting in conversion of the monoanionic {P,C − ,N} framework into a dianionic {P,C − ,C − } ligand set. The dinuclear hydroxide-bridged species (PCN H )Pd(μ-OH)Pd(PCC) was the final product obtained under ambient conditions. The "rollover" activation was followed via 31 P{ 1 H} NMR spectroscopy, and dinuclear cationic μ-OH and monomeric Pd II hydroxide intermediates were identified. DFT computational analysis of the process (M06//6-31G*, THF) showed that the energy barriers for the pyrazolyl rollover and for C−H activation through a σ-bond metathesis reaction are low enough to be overcome under ambient-temperature conditions, in line with the experimental findings. In contrast to the PCN H system, no "rollover" reactivity was observed in the PCN Me system, and the terminal hydroxide complex (PCN Me )Pd(OH) could be readily isolated and fully characterized. ■ INTRODUCTIONThe use of pincer-ligated transition-metal complexes as catalysts for organic transformations has grown dramatically in recent years. 1 The robust tridentate binding motif coupled with the tunability of the steric and electronic parameters of pincer ligands has proven highly effective in stabilizing and allowing isolation of a variety of uncommon types of metal complexes. For example, pincer ligands have been very useful in the preparation of mononuclear late-metal complexes bearing M−OR and M−NR 2 bonds. Notably, there are significantly fewer mononuclear late-transition-metal hydroxide, alkoxide, and amide complexes relative to their metal alkyl (M−C) analogues. 2 However, such M−OR and M−NR 2 linkages are pertinent to catalysis, 3,4 and thus isolation and study of model metal hydroxide, alkoxide and amide complexes are of great value.The variety of available pincer ligands has increased in recent years. While early pincer ligands were symmetric with respect to ligand "arms" (e.g., PCP, PNP, POCOP, etc.), 5 pincer-type complexes bearing unsymmetrical arms have begun to appear in greater numbers (NCC, PNN, PCO, PCS, etc.). 6 PCN-type systems in particular are intriguing, because in (PCN)M(L) n complexes (M = transition metal; L = ancillary ligand) the tridentate hybrid ligand contains both hard (N) and soft (P) donor functions, thus leading to novel and unprecedented chemical properties. 7 In such species, there is a marked difference in the trans effect between the two different donor arms. This difference results in the group with the weaker trans effect (N) being more likely to dissociate fro...

A bisimidazole-phosphine ligand, PhP-[(CH 2 ) 2 Im ArMe2 ] 2 , has been prepared and has been metalated using [Cp*Ru(μ 3 -Cl)] 4 , generating a bis(N-heterocyclic carbene)-phosphine Ru(II) species through ligand coordination followed by tautomerization. This is the first example of an NHC−donor−NHC complex with two unsubstituted N− H wingtips. Furthermore, a second metal center was installed by deprotonation of both N−H wingtips and subsequent salt metathesis to generate Ru(II)−Fe(II) and Ru(II)−Co(II) bimetallic complexes.

A Ru­(NH-NHC) complex with an open coordination site on the metal center adjacent to ligand N–H moieties has been synthesized and characterized. This complex exhibits unique reactivity upon reaction with either CO2 or NaHCO3, yielding a formate-bridged bimetallic complex via a spontaneous deoxygenation reaction and formal reduction at carbon. Dehydrogenation of the formate complex leads to a Ru–carbamate species following carbon–nitrogen bond formation between the CO2 moiety and the NHC ligand. This reactivity opens up new pathways for CO2 reduction and is relevant to H2 storage.

A facile, one pot synthesis of a coordinatively unsaturated ruthenium complex supported by a tripodal, protic bis(N-heterocyclic carbene) phosphine ligand is presented. A number of coordination complexes were discovered en route during this synthesis, revealing some of the unique aspects of complexes ligated by this type of tridentate, protic bis(NHC) ligand. Through a combination of 1D and 2D NMR spectroscopic analysis and single crystal X-ray diffraction, we reveal the intermediacy of phosphine-ligated bisimidazole complexes and show that abstraction of inner-sphere halide ions facilitates conversion to the desired tridentate bis(NHC) coordination mode. Ultimately the use of N-methyl-2-pyrrolidone is shown to enable the use of the extreme temperatures needed to facilitate the direct, thermally activated tautomerization reaction that gives rise to the bis(NHC) motif.