Syntheses and structures of cyclopentadienyl arsenic compounds II. Pentamethyl- and tetraisopropylcyclopentadienyl arsenic amido derivatives

X-(Diiodoarsanyl)benzoic acid (X = 3 and 4)

The title compounds, 4-(diiodoarsanyl)benzoic acid, (I), and 3-(diiodoarsanyl)benzoic acid, (II), both [As(C(7)H(5)O(2))I(2)], which possess a -COOH coordinating group, form molecular crystal structures composed of hydrogen-bonded dimers, the packing differences of which are caused by the relative position of the diiodoarsanyl groups. The para isomer, with Z' = 1, crystallizes in a layered structure with shortened contacts of the As atoms to only the arene rings of adjacent molecules. In contrast, the meta isomer, with Z' = 3, forms separate rectangular blocks of three ribbons, each composed of dimeric molecular units positioned almost directly above each other and with the As atoms possessing only two As···I contacts to the I atoms of neighbouring molecules.

Chemistry of pnictogen(iii)–nitrogen ring systems

This critical review covers significant recent advances in the chemistry of pnictogen(III)-nitrogen ring systems, also known as cyclopnict(III)azanes. The synthetic methodologies and reactions of the heavier pnictogen systems are compared with the well-developed chemistry of cyclophosph(III)azanes. Particular attention is focused on ring-oligomerization processes and the use of four-membered E(2)N(2) rings as building blocks for the synthesis of macrocyclic molecules. Main-group element and transition-metal complexes are also discussed (95 references).

Dissociation of 2,4-Bis(2,4,6-tri-tert-butylphenyl)-cyclo-1,3-dipnicta-2,4-diazanes (pnict = P, As, Sb) Imposed by Substituent Steric Strain: A Cyclobutane/Olefin Analogy

Three 2,4-bis(Mes)-cyclo-1,3-dipnicta-2,4-diazanes, 2PnX, have been synthesized as 1,3-dichloro- (Pn = As; X = Cl) or 1,3-bis(triflato)- (Pn = P, Sb; X = OTf) derivatives (Mes = 2,4,6-tri-tert-butylphenyl; OTf = triflato = trifluoromethanesulfonoxy). The compounds have been structurally characterized as cyclodimers, but spectroscopic characterization of melts and solutions indicates facile dissociation of the diphosphadiazane 2POTf derivative to give the corresponding iminophosphine 1POTf and of the diarsadiazane 2AsCl derivative to give the corresponding iminoarsine 1AsCl. 1,3-Bis(triflato)-2,4-bis(Mes)-cyclo-1,3-distiba-2,4-diazane (2SbOTf) does not dissociate in the melt or in solution. The presence of the sterically bulky Mes substituent does not preclude association of N-Pn olefin analogues to give single bonded cyclobutane analogues. The facile dissociation of 2POTf and isolation of 1POTf implicates a relatively high degree of substituent steric strain in the dimer. In comparison, dissociation of 2AsCl is only apparent in the melt and in solution, likely the result of the lower substituent strain in the larger N(2)As(2) framework. The largest N(2)Pn(2) framework in 2SbOTf provides sufficient space for the Mes substituents, and the monomer is not observed under the conditions examined.

Identification of new N-Sb topologies: understanding the sequential dehydrochloride coupling of primary amines and trichloropnictines

Subtle steric strain imposed by 2,6-dimethylphenyl substituents on N-Sb frameworks has enabled identification of the first acyclic dipnictadiazane and the first six-membered cyclotristibatriazane providing insight into the dehydrohalide coupling reaction of amines with halopnictines.

Synthesis of cyclo-2,4,6-Triarsa-1,3,5-triazanes from cyclo-2,4-Diarsa-1,3-diazanes Demonstrating the General Influence of Substituent Steric Strain on the Relative Stability of Pnictazane Oligomers

2,4-Dichloro-1,3-diaryl-cyclo-2,4-diarsa-1,3-diazanes (aryl = 2,6-dimethylphenyl, Dmp, or 2,6-diisopropylphenyl, Dipp) have been transformed into the corresponding 2,4,6-trichloro-cyclo-2,4,6-triarsa-1,3,5-triazanes on reaction with GaCl(3) followed by 4-(dimethylamino)pyridine (DMAP). The nitrogen bound Dmp and Dipp substituents impose "medium" substituent steric strain on the heterocycles influencing the relative thermodynamic stability of potential oligomers in favor of the trimers. This ring expansion disproportionation reaction is initiated by chloride ion abstraction, and the intermediate 2,4-dichloro-1,3,5-tris(2,6-diisopropylphenyl)-cyclo-2,4-diarsa-1,3,5-triazane-6-arsenium tetrachlorogallate has been isolated and structurally characterized. Subsequent reaction with 4-(dimethylamino)pyridine (DMAP) effects release of chloride ion from the gallate anion and consequential formation of a covalent As-Cl bond in the trimer. The observations are analogous to those for the phosphorus derivatives demonstrating a general applicability of this new synthetic procedure for the development and diversification of cyclopnictazane chemistry.

Synthesis and characterization of an homologous series of bis(amido)diazadipnictetidines (Pnict = P, As, Sb, Bi)

Spectroscopic and structural features are presented for the first homologous series of diazadipnictetidines, which have the general formula [DipNPnN(H)Dip]2 (Pn = P, As, Sb, Bi; Dip = 2,6-diisopropylphenyl). The compounds are obtained from a general reaction of the corresponding halopnictine with excess LiN(H)Dip, which was previously reported for [DipNBiN(H)Dip]2. However, isolation is improved by the introduction of LiN(H)-t-Bu (at the appropriate stoichiometry) following the addition of LiN(H)Dip. The intermediate steric presence of the Dip substituent is suitable to support the heterocatenate framework for all homologues. This is in contrast to the small substituents (e.g. alkyl), which enable both bis- and tris-amination, and the larger substituent (Mes* = tri-tert-butylphenyl), which can impose coordinative unsaturation (aminoiminopnictine) for the smaller congeners (P and As).Key words: phosphorus, arsenic, antimony, bismuth, phosphazanes, phosphetidines, synthesis, structures, spectroscopic characterization.