Solid-State and Dynamic Solution Behavior of a Cationic, Two-Coordinate Gold(I) π-Allene Complex

Abstract

Summary: The cationic gold π-allene complex {[P(t-Bu) 2 obiphenyl ]Au[η 2 -H 2 CdCdC(CH 3 ) 2 ]} þ SbF 6 -was isolated in 98% yield from reaction of 3-methyl-1,2-butadiene with a mixture of [P(t-Bu) 2 o-biphenyl]AuCl and AgSbF 6 and was characterized by X-ray crystallography and variable-temperature NMR spectroscopy. These studies revealed preferential binding of gold to the less substituted CdC bond of the allene in both the solid state and solution and also revealed fluxional behavior consistent with π-face exchange of the allene ligand via an η 1 -C2 allene intermediate or transition state.Over the past 10 years considerable progress has been made in the utilization of soluble gold complexes, in particular cationic gold(I) complexes, as catalysts for the electrophilic activation of C-C multiple bonds. 1 Allenes have played a central role in the development of this chemistry, not only as substrates but also as intermediates and products. 1 Although it is widely assumed that gold π-allene complexes are generated as reactive intermediates in these transformations, no well-defined gold π-allene complex has been documented. 2 As such, information regarding the structure and behavior of gold π-allene complexes is limited to that provided by recent computational studies 3,4 or gleaned from related transition metal π-allene complexes [5][6][7][8][9][10] and gold π-complexes. 11,12 Here we report the synthesis, X-ray crystal structure, and fluxional behavior of a cationic, two-coordinate gold(I) π-allene complex.Reaction of 3-methyl-1,2-butadiene with a mixture of [P(t-Bu) 2 o-bipheny]AuCl (1) and AgSbF 6 (1:1) employing a procedure similar to that used for the synthesis of cationic gold(I) π-alkene complexes 12 (excess allene, room temperature, ∼12 h) led to formation of black suspensions that contained only traces of*To whom correspondence should be addressed. E-mail: rwidenho@ chem.duke.edu.(

Synthesis and Study of Cationic, Two‐Coordinate Triphenylphosphine– Gold–π Complexes

“…It is worth noting that the energy barrier for intermolecular 3-hexyne exchange with 6·SbF 6 is ! 6 kcal mol À1 lower than the energy barriers determined for the intermomolecular p-ligand exchange with [P- [9,12] This difference presumably reflects both the diminished steric environ- …”

“…[6] Due to the central role of gold-p complexes in these mechanisms, there has been recent interest in the synthesis and study of cationic, two-coordinate gold-p complexes. [7] From these efforts, a number of mononuclear, cationic gold(I) complexes containing a p alkene, [8,9] alkyne, [10,11] allene, [12] conjugated diene, [13,14] or arene [15,16] p ligand and a sterically hindered, electron-rich supporting ligand, such as 1,3-bis- 3 , or PA C H T U N G T R E N N U N G (tBu) 2 -o-biphenyl, have been isolated and characterized both in the solid state and in solution. Conversely, mononuclear, cationic, two-coordinate goldp complexes containing a triphenylphosphine ligand have not been isolated.…”

“…We found the broad range of chemical shifts disconcerting given the narrow range of phosphorous chemical shifts (d = 65 AE 3 ppm) observed for a family of more than 30 complexes of the form {[PA C H T U N G T R E N N U N G (tBu) 2 -o-biphenyl]AuA C H T U N G T R E N N U N G (p ligand)} + SbF 6 À . [9,[11][12][13][14][15] Furthermore, the lower frequency value of d = 28 ppm is similar to that of weak s complexes, such as [(PPh 3 )AuOTf] [24] and [(PPh 3 )AuNTf 2 ], [25] whereas the higher frequency value of d = 45 ppm is similar to the bis(phosphine) cation [(PPh 3 ) 2 Au] + (2) ( Table 1), complexes that could be envisioned as byproducts or decomposition products in the generation of triphenylphosphine-goldp complexes. [26,27] Perhaps best characterized of these tri-…”

Synthesis of Allenes Bearing Phosphine Oxide Groups and Investigation of Their Reactivity toward Gold Complexes

“…Fürstneri solated ac omplex between tetradimethylaminoallene and Ph 3 PAuSbF 6 featuring h 1 central coordination [8] while Widenhoefer has also reported an X-ray crystal structure of the h 2 dimethylallene-Au + + PPh 3 complex. [9] Our objective wast ou se allenylphosphine oxides IV as probes for twot ypes of applications.T he first aim was the generation of new gold coordination complexes,p ossibly implying the phosphineo xide moiety. [10] These could be new precatalytic species or modelso fp roposedi ntermediates.T he second objective was to involve these substratesi nc ycloisomerization reactions when using appropriate Rs ubstituent on IV in order to deliver new phosphorus-containing chiral substrates.…”

Mechanistic insights and functionalization of alkynes in homogeneous gold catalysis.

“…As expected, hydrogen bond acceptors with lower gold affinity (e.g., DMPU, DMF) [141][142][143][144][145][146][147][148] enhanced the rate of reaction (Scheme 14b), and ionic hydrogen bond acceptors (e.g., Bu4N Other research groups reported that certain compounds improved the chemical yields in selected gold catalyzed reactions. 153,154 One notable example is the …”