The cycloheptatrienyl molybdenum alkynyl complex [Mo(CCH)(dppe)(η-C7H7)], 1 (dppe = Ph2PCH2CH2PPh2), undergoes oxidative dimerization on reaction with [FeCp2]PF6 in thf at −78 °C to give the bis(vinylidene) [{Mo(dppe)(η-C7H7)}2(μ-CCH-CHC)][PF6]2, [2][PF6]2. Deprotonation of [2][PF6]2 with KOBut yields butadiyndiyl-bridged [{Mo(dppe)(η-C7H7)}2(μ-CC-CC)], 3, which undergoes in situ aerial oxidation to give [{Mo(dppe)(η-C7H7)}2(μ-C4)][PF6], [3]PF6, as the major product. The cyclic voltammogram of [3]PF6 exhibits a series of four redox processes indicative of sequential formation of [{Mo(dppe)(η-C7H7)}2(μ-C4)] n+ (n = 0, 1, 2, 3, 4) with the comproportionation constant, K C, for [3]PF6 of 1.9 × 107. Spectroscopic investigations on [3]PF6 by IR, Raman, NIR, and EPR spectroscopy reveal properties characteristic of a d5/d6 mixed valence complex with a localized electronic structure and an estimated intramolecular electron transfer rate in the range 108–1010 s–1. The experimental NIR spectrum of [3]PF6 is consistent with the predicted spectral characteristics of a three-state model for bridge-mediated, electron transfer in a weakly coupled, symmetrical mixed valence system. The dication [3][PF6]2 was isolated by chemical oxidation and structurally characterized; magnetic susceptibility measurements on [3][PF6]2 in the temperature range 2–300 K reveal strong antiferromagnetic coupling with the exchange coupling constant J ab (defined according to the Hamiltonian Ĥspin = –J ab ·Ŝa ·Ŝb) determined as −406 (±3) cm–1.

Two series of extended carbon chain butadiynyl and hexatriynyl complexes, [Mo{(CC) n CCSiMe3}(bpy)(η-C7H7)] (n = 1, 2; bpy = 2,2′-bipyridine) and [Mo{(CC) n CCR}(dppe)(η-C7H7)] (n = 1, R = H, SiMe3; n = 2, R = SiMe3; dppe = Ph2PCH2CH2PPh2), have been prepared and structurally characterized. The redox chemistry of these complexes has been investigated by cyclic voltammetry, and the 17-electron radical cations resulting from one-electron oxidation have been characterized by spectroelectrochemical IR and UV–visible methods and EPR spectroscopy. DFT calculations on the H-terminated model complexes [Mo{(CC) n CCH}(L2)(η-C7H7)] z+ (L2 = bpy, dppe) reveal a largely metal-centered HOMO (z = 0) with a modest increase in carbon chain character with increasing chain length. Spin density calculations for the 17-electron radical cations (z = 1) show large coefficients of spin density at the metal center, consistent with the remarkably high stability of the experimental complexes. However, both DFT theoretical and experimental synthetic studies highlight a distinction between the bpy- and dppe-supported systems. The 17-electron complexes [Mo{(CC) n CCSiMe3}(bpy)(η-C7H7)]PF6 (n = 1, 2) are unique examples of isolable, metal-stabilized butadiynyl and hexatriynyl radicals. In contrast, the dppe radical [Mo(CCCCSiMe3)(dppe)(η-C7H7)]+ exhibits chain-centered reactivity, consistent with enhanced coefficients of spin density at Cβ and Cδ in the model complex [Mo(CCCCH)(dppe)(η-C7H7)]+.

The identification of carbohydrate-protein interactions is central to our understanding of the roles of cell-surface carbohydrates (the glycocalyx), fundamental for cell-recognition events. Therefore, there is a need for fast high-throughput biochemical tools to capture the complexity of these biological interactions. Here, we describe a rapid method for qualitative label-free detection of carbohydrate-protein interactions on arrays of simple synthetic glycans, more complex natural glycosaminoglycans (GAG), and lectins/carbohydrate binding proteins using matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry. The platform can unequivocally identify proteins that are captured from either purified or complex sample mixtures, including biofluids. Identification of proteins bound to the functionalized array is achieved by analyzing either the intact protein mass or, after on-chip proteolytic digestion, the peptide mass fingerprint and/or tandem mass spectrometry of selected peptides, which can yield highly diagnostic sequence information. The platform described here should be a valuable addition to the limited analytical toolbox that is currently available for glycomics.

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