We present the synthesis of a zwitterionic triphosphenium molecule, Bu(CH)(PPh)P (L), which can act as a single- or multidentate ligand with group 6, 7, 8 and 9 metal carbonyl complexes. Group 6, [M(CO)L] complexes are formed under photolytic conditions, where the metal is bound at the P(i) center. In the case of Mo(CO), the bimetallic complex [M(CO)LMo(CO)] is generated, which features bonds to both the phosphorus(i) center and the cyclopentadienyl moiety of the molecule. Interestingly, group 7 and 9 metal carbonyl dimers generate bimetallic complexes in the form [M(CO)L], where both metal centers are bound at the phosphorus(i) center. A detailed analysis of these molecules is provided, including X-ray diffraction, multinuclear NMR, infrared spectroscopy and computational investigations.
We present herein the optimized synthesis of a triphosphenium bromide salt. Apart from being a versatile metathesis reagent, this unusually stable low-valent-phosphorus-containing compound acts as a useful P transfer agent. Unlike traditional methods employed to access low-coordinate phosphorus species which usually require pyrophoric phosphorus-containing precursors (white phosphorus, Tris(trimethylsilyl)phosphine, etc.), or harsh reducing agents (alkali metals, potassium graphite, etc.), the current approach does not involve pyrophoric or explosive reagents and can be done on large scales (>20 g) in excellent yields by undergraduates with basic air-free synthetic training. The bromide counter ion is readily exchanged with other anions such as tetraphenyl borate (described herein) using typical salt metathesis reagents to obtain materials with desired properties and reactivities. The versatility of this P transfer approach is exemplified by the reactions of these triphosphenium precursors with an N-heterocyclic carbene and an anionic bisphosphine, each of which readily displace the neutral bisphosphine to give an NHC-stabilized phosphorus(I) cation and a phosphorus(I) containing zwitterion, respectively.
Treatmento ft wo equivalents of the triphosphenium zwitterion L with sources of Ni 0 and Pd 0 form the mononuclear h 2 -diphosphoniodiphosphene complexes 1 and 2.T he reactionb etween L and [FeCp(CO) 2 ] 2 resultsi n the binuclear m-h 1 :h 1 -diphosphoniodiphosphene iron complex 3,w hich features an alternative bondingm otif of the diphosphoniodiphosphene unit. The formation of these speciesh as been confirmed by spectroscopic methods and single-crystal X-ray diffraction analysis, and their electronic structures have been elucidated using computational methods.Tremendous strides have been made in oligophosphorus chemistry over the past few decades. [1] An importants ubset of mixed coordinateP ÀPb onded compounds are so-called triphosphenium ions (Figure 1). [2] Anionic variants were first reported by Fluck, [3] and Schmidpeter subsequently developed the first cationic derivatives. [4,5] Since that time, the reactivity of the PPP fragment has been well developed by several groups,i ncluding our own. [6][7][8][9][10][11][12] In spite of typicallyb eing drawn as having two lone pairs on the dicoordinate phosphorus atom (cf. phosphanides), triphosphenium cationsa re poor nucleophiles. This observation is exemplified by their inability to form isolable metal complexesa nd it has been rationalized by two factors:t heir overall positive charge, which stabilizes the highest occupied molecular orbital( HOMO), and the strong negative hyperconjugation( p-backbonding) of electron density from the centralp hosphorus atom into the flanking phosphines. [8] To overcome this deficiency,t he Ragogna group designed az witterionic triphosphenium that incorporates a negativelyc harged borate functionality into the backbone. [13,14] Apart from enhancing solubility,t hey demonstrated that this also enhancest he nucleophilicity of the central phosphorus atom and thus they were able to isolatet he first examples of triphosphenium metal complexes.O ur groupp ut forward another design for az witterionic triphosphenium incorporating a cyclopentadienide (Cp) fragment into the backbone. [15] Indeed, we were able to isolate many mono-andb i-metallic complexeso fL (see Figure 1), [16] but we were met with particularly interesting results while investigating L'sc oordinationc hemistry with late transitionm etals.Ta rgeting the complex NiL 2 ,t wo equivalents of L were reacted with one equivalent Ni(COD) 2 .E xamination of the 31 PNMR spectrum of the reactionm ixture gave ar emarkably clean spectrum,w hich featured ac omplex pattern with three second-order multiplets centered at À90.5, 9.5, and 15.3 ppm (Figure 2). The magnetic inequivalence apparent by these signals as well as the introduction of an ew chemically unique phosphorus environment suggested the formation of aP ÀPi nsertionp roduct, which would render the two phosphonio fragmentso ft he triphosphenium chemically inequivalent. Perplexingly,m ass spectrometry performedo nas ample of this product gave am olecular ion peak consistent with the composition NiL 2 ,t hough this speciesc ould ...
The synthesis of novel bis(trithio)phosphines is achieved by oxidative addition of tetrathiocins to the phosphorus(i) reagent [Pdppe][Br] in good yields under ambient conditions. These bis(trithio)phosphines and the related intermediate diphosphine species are characterized by X-ray diffraction and multinuclear NMR and a mechanism is proposed for the formation of these molecules. In contrast, the related reaction with diphenyldisulfide produces a mononuclear tris(phenylthio)phosphine.
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