Synthesis, reactivity, and computational analysis of halophosphines supported by dianionic guanidinate ligands

The reported chemistry and reactivity of guanidinate supported group 15 elements in the +3 oxidation state, particularly phosphorus, is limited when compared to their ubiquity in supporting metallic elements across the periodic table. We have synthesized a series of chlorophosphines utilizing homo- and heteroleptic (dianionic)guanidinates and have completed a comprehensive study of their reactivity. Most notable is the reluctancy of these four-membered rings to form the corresponding N-heterocyclic phosphenium cations, the tendency to chemically and thermally eliminate carbodiimide, and the scarcely observed ring expansion by insertion of a chloro(imino)phosphine into a P-N bond of the P-N-C-N framework. Computational analysis has provided corroborating evidence for the unwillingness of the halide abstraction reaction by demonstrating the exceptional electron acceptor properties of the target phosphenium cations and the underscoring strength of the P-X bond.     

Inhibited chelation in the new gamma-phosphino-beta-diketiminate to give phosphine --> arsine coordination

A gamma-diphenylphosphino-beta-diketimine has been synthesised and the 31P NMR handle allows for in situ analysis of reaction mixtures revealing unprecedented reactivity with AsCl3 to give a novel phosphinoarsine intramolecular coordination complex.     

Transformations between monomeric,dimeric, and trimeric phosphazanes: oligomerizing NP analogues of olefins

Isolation and characterization of a crystal mixture of iminophosphine 1 and diphosphazane 2 (R = Mes*, X = OTf) is enabled by the steric interactions between bulky substituents implicating monomer/dimer 1/2 equilibria and the conclusion is supported by the observation of a ring-expansion reaction to give a triphosphazane 3 (R = Dipp, X = Cl).     

Z4-Kerdock Codes, Orthogonal Spreads, and Extremal Euclidean Line-Sets

When m is odd, spreads in an orthogonal vector space of type⁺(2m + 2,2) are related to binary Kerdock codes and extremalline-sets in 2^{m + 1} with prescribed angles. Spreads in a 2m-dimensionalbinary symplectic vector space are related to Kerdock codesover Z₄ and extremal line-sets in with prescribed angles. These connections involve binary, realand complex geometry associated with extraspecial 2-groups.A geometric map from symplectic to orthogonal spreads is shownto induce the Gray map from a corresponding Z₄-Kerdock codeto its binary image. These geometric considerations lead tothe construction, for any odd composite m, of large numbersof Z₄-Kerdock codes. They also produce new Z₄-linear Kerdockand Preparata codes. 1991 Mathematics Subject Classification:primary 94B60; secondary 51M15, 20C99.     

Synthesis and structures of complexes demonstrating the coordinative versatility of the 2,4-diimino-3-phosphinopentene anion (gamma-phosphino-beta-diketiminate)

The synthesis and characterization of a 2,4-diimino-3-phosphinopentene anion (gamma-phosphino-beta-diketiminate) is reported and enables diversification of the beta-diketiminate ligand framework, which has been widely employed across the periodic table. Phosphines are observed to adopt the gamma-position of the ligand rather than the N,N' chelate. While aluminum and lithium adopt the familiar N,N' chelate arrangement with the new 2,4-diimino-3-phosphinopentene anion ligand, reactions with AsCl(3) or SbCl(3) result in substitution at the beta-methyl position on the ligand backbone, realizing novel P-->E (E = As or Sb) intramolecular coordination. The chemistry of the 2,4-diimino-3-phosphinopentene anion can be monitored by the (31)P NMR chemical shifts, which are distinctively diagnostic of the coordinative engagement of the ligand.     

Application of Combinatorial Procedures in the Search for Serine-Protease-Like Activity with Focus on the Acyl Transfer Step

Recursive deconvolution of a 729-membered peptide library has identified three active sequences, in which both Ser and His are present in one of the two tripeptidic chains generated on a steroidal scaffold (see structural formula), for the cleavage of an activated p-nitrophenyl ester. This combinatorial approach aims at searching for serine-protease-like activity.