Studies on gas-phase cyclometalations of [ArNi(PPh₃)n]⁺ (n = 1 or 2) by electrospray ionization tandem mass spectrometry

Abstract

Gas-phase cyclometalation of [ArNi(PPh 3 ) n ] ϩ (n ϭ 1, 2) complexes have been studied by ESI-MS/MS. The electron-donating substituents of aromatic iodides in the para position were found to inhibit the cyclometalation process of losing ArH, while the electron-withdrawing substituents in the para position were found to enhance it. These results indicate that the cyclometalation process of losing ArH is favored by electron-deficient aromatic groups. In addition, the detailed dissociation pathways of the cationic nickel complexes were studied, and among these pathways, the process of aryl-aryl interchange was also found to proceed in ESI-MS/MS. (J Am Soc Mass Spectrom 2010, 21, 1265-1274) © 2010 American Society for Mass Spectrometry C yclometalation occurs when a ligand on an organo-metal complex undergoes an intramolecular metalation with concomitant formation of a chelate ring containing a metal-carbon bond [1]. This kind of transformation has attracted significant attention over the past three decades [2][3][4][5][6][7]. On the one hand, cyclometalation can be detrimental to a desired reaction course and can be prevented by a variety of techniques to improve catalytic efficiency of the metal complex. As cyclometalation methodology has been developed, a number of cyclometalated complexes were employed successfully in organic synthesis [8,9], catalysis [10 -12], and photochemistry [13][14][15]. Mechanisms for the cyclometalation associated with C-H bond cleavage have been proposed [16 -21], and three related mechanisms for C-H bond cleavage are typically accepted: oxidative addition, electrophilic substitution, and multicentered pathways (such as -bond metathesis) [22][23][24][25][26]. The actual mechanisms that pertain for cyclometalation of a given metal complex are highly dependent on the exact nature of the metal complexes, identities of hydrocarbon substituents, solvents involved, and specific operating conditions [21]. As a result, a complete understanding and description of the general mechanism are still lacking, and more data are needed before we can fully describe critical reactivity patterns.The focus to date has been on the study of solutionphase cyclometalations, but gas-phase cyclometalations have recently received more attention [27][28][29]. Generally, gas-phase studies conducted with tandem mass spectrometry (MS/MS) on extremely small sample quantities can theoretically ascertain the propensity for a complex to undergo certain kinds of reactions. The energy conditions and dissociation pathways provide useful insights, with applicability to related solutionphase reactions [30 -40]. Based on the gas-phase methodologies, Henderson and coworkers published their investigation of the cyclometalation of palladium(II) and platinum(II) diphosphine complexes MCl 2 (Ph 2 P (CH 2 ) 5 PPh 2 ) in 2004 [28]. More recently, Schwarz and coworkers explored the whole process of cyclometalation of 2,2=-bipyridine platinum(II) complexes in gas phase by a combination of gas-phase methodologies and theoretical calcu...

Pd8 Nanocluster with Nonmetal‐to‐Metal‐ Ring Coordination and Promising Photothermal Conversion Efficiency

“…Moreover, the apparent peak at m/z 2,466.60 was attributed to [Pd 8 (PPh) 2 PPh 3 (S-Adm) 6 + Cs] + (deviation: 0.15), representing a fragment derived from the mother ion subsequent to the removal of one PPh 3 ligand. [17] The numbers of Cs + in the formulas are equal to the ion charge numbers, indicating the neutrality of the as-obtained species, which is further supported by the fact that no rational signal was found in the mass spectra without the addition of Cs + . Thus, the formula of the as-obtained Pd nanoclusters was concluded to be Pd 8 (PPh) 2 (PPh 3 ) 2 (S-Adm) 6 (denoted as Pd 8 -S).…”