On the reaction of Ph2PNHPPh2 with RNCS (R = Et, Ph, p-NO2C6H4): Preparation of the zwitterionic ligand EtNHC(S)Ph2P=NPPh2C(S)NEt (HSNS) and the zwitterionic metalate [(SNS)Rh(CO)]

Mattia Asti, Roberto Cammi, Daniele Cauzzi, Claudia Graiff, Roberto Pattacini, Giovanni Predieri, Alessandro Stercoli, Antonio Tiripicchio

Research output: Contribution to journalArticlepeer-review

Abstract

The reaction of Ph2PNHPPh2 (PNP) with RNCS (Et, Ph, p-NO2-(C6H4)) gives addition products resulting from the attack of the P atoms of PNP on the electrophilic carbon atom of the isothiocyanate. When PNP is reacted with EtNCS in a 1:2 molar ratio, the zwitterionic molecule EtNHC(S)PPh2=NP+Ph 2C(S)N-Et (HSNS) is obtained in high yield. HSNS can be protonated (H2SNS+) or deprotonated (SNS-), behaving in the latter form as an S,N,S-donor pincer ligand. The reaction of HSNS with [(acac)Rh(CO)2] (acac = acetylacetonate) affords the zwitterionic metalate [(SNS)Rh(CO)]. Other products can be obtained depending on the R group, the PNP/RNCS ratio (1:1 or 1:2), and the reaction temperature. The proposed product of the primary attack of PNP on RNCS, Ph2PN=PPh2C(S)NHR (A), cannot be isolated. Reaction of A with another RNCS molecule leads to 1:2 addition compounds of the general formula RNHC(S)PPh2=NP+ Ph2C(S)N-R (1), which can rearrange into the non-zwitterionic product RNHC(S)PPh2=NP(S)Ph2 (2) by eliminating a molecule of RNC. Two molecules of A can react together, yielding 1:1 PNP/RNCS zwitterionic products of the formula RNHCH[PPh2= NP(S)Ph 2]PPh2=NP+Ph2C(S)N-R (3). Compound 3 can then rearrange into RNHCH[PPh2=NP(S)Ph 2]2 (4) by losing a RNC molecule. When R = Et (a), compounds 1a, 2a (HSNS), and 4a have been isolated and characterized. When R = Ph (b), compounds 2b and 4b can be prepared in high yield. When R = p-NO 2C6H4 (c), only compound 3c is observed and isolated in high yield. The crystal structures of HSNS, [(SNS)Rh(CO)], and of the most representative products have been determined by X-ray diffraction methods.

Original languageEnglish
Pages (from-to)3413-3419
Number of pages7
JournalChemistry - A European Journal
Volume11
Issue number11
DOIs
Publication statusPublished - May 20 2005

Keywords

  • Heterocycles
  • Rhodium
  • Synthetic methods
  • Tridentate ligands
  • Zwitterions

ASJC Scopus subject areas

  • Chemistry(all)

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