Marcin Gonsior

PX4+, P2X5+, and P5X2+ (X: Br, I) Salts of the Superweak Al(OR)4- Anion [R: C(CF3)3].

PX(4) (+)[Al(OR)(4)](-) (X=I: 1 a, X=Br: 1 b) was prepared from X(2), PX(3), and Ag[Al(OR)(4)] [R=C(CF(3))(3)] in CH(2)Cl(2) at -30 degrees C in 69-86 % yield. P(2)X(5) (+) salts were prepared from 2 PX(3) and Ag[Al(OR)(4)] in CH(2)Cl(2) at -30 degrees C yielding almost quantitatively P(2)X(5) (+)[Al(OR)(4)](-) (X=I: 3 a, X=Br: 3 b). The phosphorus-rich P(5)X(2) (+) salts arose from the reaction of cold (-78 degrees C) mixtures of PX(3), P(4), and Ag[Al(OR)(4)] giving P(5)X(2) (+)[Al(OR)(4)](-) (X=I: 4 a, X=Br: 4 b) with a C(2v)-symmetric P(5) cage. Silver salt metathesis presumably generated unstable PX(2) (+) cations from PX(3) and Ag[Al(OR)(4)] (X=Br, I) that acted as electrophilic carbene analogues and inserted into the Xbond;X (Pbond;X/Pbond;P) bond of X(2) (PX(3)/P(4)) leading to the highly electrophilic and CH(2)Cl(2)-soluble PX(4) (+) (P(2)X(5) (+)/P(5)X(2) (+)) salts. Reactions that aimed to synthesize P(2)I(3) (+) from P(2)I(4) and Ag[Al(OR)(4)] instead led to anion decomposition and the formation of P(2)I(5)(CS(2))(+)[(RO)(3)Al-F-Al(OR)(3)](-) (5). All salts were characterized by variable-temperature solution NMR studies (3 b also by (31)P MAS NMR), Raman and/or IR spectroscopy as well as X-ray crystallography (with the exception of 4 a). The thermochemical volumes of the Pbond;X cations are 121 (PBr(4) (+)), 161 (PI(4) (+)), 194 (P(2)Br(5) (+)), 271 (P(2)I(5) (+)), and 180 A(3) (P(5)Br(2) (+)). The observed reactions were fully accounted for by thermochemical calculations based on (RI-)MP2/TZVPP ab initio results and COSMO solvation enthalpy calculations (CH(2)Cl(2) solution). The enthalpies of formation of the gaseous Pbond;X cations were derived as +764 (PI(4) (+)), +617 (PBr(4) (+)), +749 (P(2)I(5) (+)), +579 (P(2)Br(5) (+)), +762 (P(5)I(2) (+)), and +705 kJ mol(-1) (P(5)Br(2) (+)). The insertion of the intermediately prepared carbene analogue PX(2) (+) cations into the respective bonds were calculated, at the (RI-)MP2/TZVPP level, to be exergonic at 298 K in CH(2)Cl(2) by Delta(r)G(CH(2)Cl(2))=-133.5 (PI(4) (+)), -183.9 (PBr(4) (+)), -106.5 (P(2)I(5) (+)), -81.5 (P(2)Br(5) (+)), -113.2 (P(5)I(2) (+)), and -114.5 kJ mol(-1) (P(5)Br(2) (+)).

A Thallium Coated Dianion: Trigonal Bipyramidal [F2Al(OR)3]2— Coordinated to Three Tl+ Cations in the Ion Pair [Tl3F2Al(OR)3]+[Al(OR)4]— [R = CH(CF3)2]

The reproducible synthesis of the unusual ionic aluminum compd. [Tl3F2Al(OR)3]+[Al(OR)4]- (1) is reported. In the reaction of Li[Al(OR)4] [R = C(H)(CF3)2] with TlF the initially desired Tl[Al(OR)4] only formed with an exact 1:1 stoichiometry, while an excess of TlF led to [Tl3F2Al(OR)3]+[Al(OR)4]- (1). Addnl. the x-ray single crystal structure of the byproduct [(ROH)TlAl(OR)3(m-F)]2 (2) was detd. Compds. 1 and 2 were characterized by x-ray single crystal structure detns. and 1 also by NMR spectroscopy and an elemental anal. In 1 the [Tl3F2Al(OR)3]+ cation forms a trigonal bipyramid with a pentacoordinate aluminum atom. Three Tl+ cations cover the [F2Al(OR)3]2- dianion core and the charge of the resulting [Tl3F2Al(OR)3]+ cation is compensated by a weakly coordinating [Al(OR)4]- anion. Compd. 2 contains a centrosym. [Al(OR)3(m-F)]22- dianion core with pentacoordinate aluminum atoms building a distorted edge sharing double trigonal bipyramid. The [Al(OR)3(m-F)]22- dianion coordinates two [Tl(ROH)]+ cations giving the non charged mol. [(R-OH)TlAl(OR)3(m-F)]2 (2). Based on BP86/SVP (DFT-) and lattice enthalpy calcns. a pathway of the reaction is proposed to rationalize the formation of the [M3F2Al(OR)3]+ cation upon reaction of Li[Al(OR)4] with MF for M = Tl but not for M = Cs (cf Cs+ and Tl+ have very similar ionic radii). Using a suitable Born-Haber cycle and in agreement with the expt., the enthalpies of the reaction of two M[Al(OR)4] with two MF giving [M3F2Al(OR)3]+[Al(OR)4]- and MOR are favorable for M = Tl by 127 kJ/mol but endothermic for the formation of the hypothetical [Cs3F2Al(OR)3]+[Al(OR)4]- by 95 kJ/mol. It is suggested that in the reaction leading to 1 initially Tl[Al(OR)4] is formed, followed by an abstraction of TlOR and Al(OR)3. The latter very strong Lewis acid reacts subsequently with an excess of TlF yielding 1. [on SciFinder (R)]

A theoretical study on the formation of EX4+ and E2X5+(E = P, As; X = Br, I) from Ag+ and EX3/X2

The mechanism and the thermodynamics of the formation of EX2+, EX4+ and E2X5+ (E = As, P; X = Br, I) was carefully analyzed with MP2/TZVPP calculations and inclusion of entropy and solvation effects (COSMO model approximating CH2Cl2). Thus, as likely intermediates the complexes of Ag+ and one or two EX3 as well as EX3/X2 were optimized. The global minimum isomers of the Ag(EX3)2+ intermediates were found to be P-coordinated Ag(PI3)2+ and (BrPBr2)Ag(PBr3)+ but exclusively halogen coordinated Ag(X2AsX)2+ complexes. Similarly complicated is the situation for the Ag(EX3)(X2)+ intermediates: (I3E)Ag(I2)+, (BrAsBr2)Ag(Br2)+ and (Br3P)(Br-Br)Ag+ complexes were found to be the global minima. Based on all available results likely mechanisms for the formation of the known PX4+, AsBr4+, P2X5+ salts (X = Br, I) from these intermediates were proposed. An explanation for the failure to prepare an AsI4+ salt is also given.