Coordination to RMg⁺ and RZn⁺ Cations¹

Abstract

Addition of a second coordinating agent (coord*) to a solution of RM(coord) + A -(R ) ethyl or neopentyl, M ) Zn or Mg, A -) 1,2,3,4-tetraphenylcyclopentadienyl) can provide equilibrium mixtures of these compounds, coord, and RM(coord*) + A -. This exchange with RMg(coord) + requires the addition of a small amount of R 2 Mg, but added R 2 Zn is not necessary for exchanges with RZn(coord) + . The equilibrium constants provide information about the relative abilities of different coordinating agents to coordinate to RM + and reveal significant differences between coordination to RMg + and RZn + . Reactions of RM(coord) + with R′ 2 M (R ) ethyl or neopentyl for RMg(coord) + and ethyl, isopropyl, tert-butyl, neopentyl, or p-methylphenyl for RZn(coord) + ) provide equilibrium mixtures of these components, R′M-(coord) + , and R 2 M. The equilibrium constants provide information about the effect of R on stability. An X-ray structure of p-methylphenylzinc (2,5,8,11-tetramethyl-2,5,8,11-tetraazadodecane) + shows that just three of the N atoms are coordinated to Zn. The effects of coord, R, and metal on RM(coord) + stability are discussed, and the abilities of coordinating agents to coordinate to RM + , to slow allylic isomerization of (CH 2 dCMeCH 2 ) 2 Zn, and to convert R 2 Zn to RZn(coord) + are compared.Coordination plays a major role in organomagnesium and organozinc chemistry. Because of a strong propensity to form additional bonds, the metal atoms of the compounds, usually written as RMgX, R 2 Mg, RZnX, and R 2 Zn (X a halogen, R alkyl or aryl), generally coordinate to functions such as alkoxy or amino when these are present, often as part of the solvent. 3,4 Additional bonds also may result from bridging of groups between metal atoms. Formation of several strong bonds between O or N atoms of a macrocycle and the Mg of the cation must provide the driving force for reactions of some macrocycles with organomagnesium compounds to produce coordinated RMg + cations and organomagnesate anions, as exemplified in eq 1. [5][6][7][8] Because of such observations, we wanted to determine the abilities of coordinating

Microsolvated and Chelated Butylzinc Cations: Formation, Relative Stability, and Unimolecular Gas‐Phase Chemistry

“…½ZnRHal ðsolvÞ Ð ½ZnR þ ðsolvÞ þ ½ZnRðHalÞ 2 À ðsolvÞ ð6Þ Related processes were reported by Richey and co-workers, who extensively studied the reactions of strongly coordinat-ing agents, such as crown ethers, azacrown ethers, and cryptands with organomagnesium [15,16] and organozinc compounds. [17] Relying on 1 H NMR spectroscopy, these authors could establish the occurrence of disproportionation reactions in benzene and ethers [Eqs. (7) and (8) with M = Mg and Zn, and coord = coordination agent].…”

“…(7) and (8) with M = Mg and Zn, and coord = coordination agent]. [15][16][17] 2 ½MgRHal þ coord Ð ½MgRðcoordÞ þ þ ½MgRðHalÞ 2 À ð7Þ…”

Structural Organozinc Chemistry

“…The synthesis and structural characterization of a compound containing p-tolylzinc cations complexed to a N,N,N,N-tetradentate ligand with a tetraphenylcyclopentadienyl anion as the counterpart has been reported 185 . It seems that all four nitrogen atoms are involved in coordination to zinc, thus giving a penta-coordinate EtZn cation.…”

Pre-inverse-crowns: synthetic, structural and reactivity studies of alkali metal magnesiates primed for inverse crown formation

“…[1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] Compared to the organolithium reagents commonly employed in these reactions, magnesiates (as well as other types of ate, most importantly zincates 1,21-45 ) can show advantages of superior functional group tolerance and application at ambient temperature and in ethereal solvents. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] Compared to the organolithium reagents commonly employed in these reactions, magnesiates (as well as other types of ate, most importantly zincates 1,21-45 ) can show advantages of superior functional group tolerance and application at ambient temperature and in ethereal solvents.…”