Junhong Fu

Phosphine, isocyanide, and alkyne reactivity at pentanuclear molybdenum/tungsten-iridium clusters

The trigonal bipyramidal clusters M2Ir3(μ-CO)3(CO)6(η(5)-C5H5)2(η(5)-C5Me4R) (M = Mo, R = Me 1a, R = H; M = W, R = Me, H) reacted with isocyanides to give ligand substitution products M2Ir3(μ-CO)3(CO)5(CNR′)(η(5)-C5H5)2(η(5)-C5Me4R) (M = Mo, R = Me, R′ = C6H3Me2-2,6 3a; M = Mo, R = Me, R′ = (t)Bu 3b), in which core geometry and metal atom locations are maintained, whereas reactions with PPh3 afforded M2Ir3(μ-CO)4(CO)4(PPh3)(η(5)-C5H5)2(η(5)-C5Me4R) (M = Mo, R = Me 4a, H 4c; M = W, R = Me 4b, H), with retention of core geometry but with effective site-exchange of the precursors’ apical Mo/W with an equatorial Ir. Similar treatment of trigonal bipyramidal MIr4(μ-CO)3(CO)7(η(5)-C5H5)(η(5)-C5Me5) (M = Mo 2a, W 2b) with PPh3 afforded the mono-substitution products MIr4(μ-CO)3(CO)6(PPh3)(η(5)-C5H5)(η(5)-C5Me5) (M = Mo 5a; M = W 5b), and further reaction of the molybdenum example 5a with excess PPh3 afforded the bis-substituted cluster MoIr4(μ3-CO)2(μ-CO)2(CO)4(PPh3)2(η(5)-C5H5)(η(5)-C5Me5) (6). Reaction of 1a with diphenylacetylene proceeded with alkyne coordination and C≡C cleavage, affording Mo2Ir3(μ4–η(2)-PhC2Ph)(μ3-CPh)2(CO)4(η(5)-C5H5)2(η(5)-C5Me5) (7a) together with an isomer. Reactions of 2a and 2b with PhC≡CR afforded MIr4(μ3–η(2)-PhC2R)(μ3-CO)2(CO)6(η(5)-C5H5)(η(5)-C5Me5) (M = Mo, R = Ph 8a; M = W, R = Ph 8b, H; M = W, R = C6H4(C2Ph)-3 9a, C6H4(C2Ph)-4), while addition of 0.5 equivalents of the diynes 1,3-C6H4(C2Ph)2 and 1,4-C6H4(C2Ph)2 to WIr4(μ-CO)3(CO)7(η(5)-C5H5)(η(5)-C5Me5) gave the linked clusters [WIr4(CO)8(η(5)-C5H5)(η(5)-C5Me5)]2(μ6–η(4)-PhC2C6H4(C2Ph)-X) (X = 3, 4). The structures of 3a, 4a–4c, 5b, 6, 7a, 8a, 8b and 9a were determined by single-crystal X-ray diffraction studies, establishing the core isomerization of 4, the site selectivity for ligand substitution in 3–6, the alkyne C≡C dismutation in 7, and the site of alkyne coordination in 7–9. For clusters 3–6, ease of oxidation increases on increasing donor strength of ligand, increasing extent of ligand substitution, replacing Mo by W, and decreasing core Ir content, the Ir-rich clusters 5 and 6 being the most reversible. For clusters 7–9, ease of oxidation diminishes on replacing Mo by W, increasing the Ir content, and proceeding from mono-yne to diyne, although the latter two changes are small. In situ UV-vis-near-IR spectroelectrochemical studies of the (electrochemically reversible) reduction process of 8b were undertaken, the spectra becoming increasingly broad and featureless following reduction. The incorporation of isocyanides, phosphines, or alkyne residues in these pentanuclear clusters all result in an increased ease of oxidation and decreased ease of reduction, and thereby tune the electron richness of the clusters.

Timing-dependent LTP and LTD in mouse primary visual cortex following different visual deprivation models

Visual deprivation during the critical period induces long-lasting changes in cortical circuitry by adaptively modifying neuro-transmission and synaptic connectivity at synapses. Spike timing-dependent plasticity (STDP) is considered a strong candidate for experience-dependent changes. However, the visual deprivation forms that affect timing-dependent long-term potentiation(LTP) and long-term depression(LTD) remain unclear. Here, we demonstrated the temporal window changes of tLTP and tLTD, elicited by coincidental pre- and post-synaptic firing, following different modes of 6-day visual deprivation. Markedly broader temporal windows were found in robust tLTP and tLTD in the V1M of the deprived visual cortex in mice after 6-day MD and DE. The underlying mechanism for the changes seen with visual deprivation in juvenile mice using 6 days of dark exposure or monocular lid suture involves an increased fraction of NR2b-containing NMDAR and the consequent prolongation of NMDAR-mediated response duration. Moreover, a decrease in NR2A protein expression at the synapse is attributable to the reduction of the NR2A/2B ratio in the deprived cortex.

Dynamic Permutational Isomerism in a closo‐Cluster

Permutational isomers of trigonal bipyramidal [W2RhIr2(CO)9(η(5)-C5H5)2(η(5)-C5HMe4)] result from competitive capping of either a W2Ir or a WIr2 face of the tetrahedral cluster [W2Ir2(CO)10(η(5)-C5 H5)2] from its reaction with [Rh(CO)2(η(5)-C5HMe4)]. The permutational isomers slowly interconvert in solution by a cluster metal vertex exchange that is proposed to proceed by Rh-Ir and Rh-W bond cleavage and reformation, and via the intermediacy of an edge-bridged tetrahedral transition state. The permutational isomers display differing chemical and physical properties: replacement of CO by PPh3 occurs at one permutational isomer only, while the isomers display distinct optical power limiting behavior.