Variable coordination of a chiral diphosphine containing an amidinium/NHC group within its backbone: μ-P,P′, κ2-P,P′ and κ3-P,C,P′ coordination modes

Abstract

A diphosphine ligand (1·HPF(6)), which is a potential precursor to a PC(NHC)P pincer, with a backbone containing two phenylene groups and a central bicyclic 4-aza-2-azoniabicyclo[3.2.1]oct-2-ene unit has been synthesised and coordinated to Pd(II) and Pt(II) to give trans-[M(κ(2)-P,P'-)Cl(2)]PF(6) where M = Pd (2) or Pt (3a). Single-crystal structure determinations of 2 and 3a show the complexes to be isostructural with the diphosphine coordinated in a trans-spanning fashion and the amidinium unit being protonated and non-coordinated. 2 and 3a react with CH(3)I to give the dimers trans-[Pd(2)(μ-1·H)(2)I(4)](PF(6))(2), 6, and trans-[Pt(2)(μ-1·H)(2)I(4)](PF(6))(2), 7, as the major products. This bridging mode of coordination of [1·H](+) is also seen in trans-[Rh(2)(μ-1·H)(1,5-COD)(2)Cl(2)]PF(6), 4, and [Pt(2)(μ-κ(2)-1·H)(dvdms)]PF(6), 5. Upon treatment with KO(t)Bu complexes and undergo deprotonation at the amidinium carbon to give trans-[M(κ(3)-P,C,P'-1)Cl]PF(6) where M = Pd (8), and Pt (9). The related trans-[Rh(κ(3)-P,C,P'-1)(CO)]PF(6) (10) is prepared directly from 1·HPF(6) and Rh(acac)(CO)(2): this and the palladium and platinum complexes 8 and 9 are isolated as isomeric mixtures as a consequence of a conformational isomerism. In situ deprotonation of 1·HPF(6) followed by addition of Ag(CF(3)SO(3)) gave S(Ag)-[Ag(κ(3)-P,C,P'-1)(CF(3)SO(3))], 11. Some preliminary studies of the reactivity of 2 and 8 in Suzuki-type reactions are reported and the Pt(0) system has been shown to be an active hydrosilylation catalyst.

Synthesis of Camphor-Derived Bis(pyrazolylpyridine) Rhodium(III) Complexes: Structure–Reactivity Relationships and Biological Activity

“…Tridentate triamine ligands have advantages, including ready availability, relatively low cost, and low toxicity . Various metal complexes with camphor-based pyridine ligands have also been used for asymmetric catalytsis and tested for biomolecular interactions or antitumor activity. − …”

Platinum catalysed hydrosilylation of propargylic alcohols

“…[41][42][43] A solution to this problem was found through the use of bulky trialkylphosphine ligands [44][45][46][47] and more recently the use of platinum N-heterocyclic carbene complexes. [48][49][50][51][52] These sterically encumbered catalysts can impart high levels of selectivity on the reactions. Of note was the development of the (dvs)Pt-Pt-Bu 3 catalyst which exhibits excellent catalytic activity and a high level of selectivity.…”

Synthesis and properties of seven- to nine-membered ring nitrogen heterocycles. Cyclic amidines and cyclic amidinium salts

“…Employing a similar methodology, Newman et al have synthetized salts containing aryl groups bearing electron donor groups as precursors of tridentate ligands. 98,99 In 2005, a method was patented in which orthoesters were used as precursors to prepare cationic polymers bearing cyclic non-aromatic units containing an amidinium group, such as tetrahydrodiazepinium salts, among others. 100 One strategy to introduce a cyclic amidinium group into a side chain of the polymer is either to start out from a polymer which bears an orthoester group 29, preferably an ethyl orthoester, in the side chain and allow it to react with an N,N'-dialkyl-α,ω-alkanediamine, or to start out from a polymer which bears the diamine function 30 in the side chain and allow it to react with an orthoester, preferably an ethyl orthoester (Scheme 31).…”

“…The first example has been reported by Cetinkaya et al, who demonstrated that in situ generated 1,3dibenzyltetrahydrodiazepin-2-ylidene palladium complexes are very effective in Suzuki-Miyaura coupling reactions of deactivated aryl chlorides. 95 Since then, seven-membered NHC complexes have been tested for catalytic transformations such as the Heck type cross-coupling, 96,105,122 Suzuki type reactions, 10,99 hydration of internal alkynes, 123 hydrosilylation, 99,104 catalytic hydrogenation 106 and transfer hydrogenation. 124,125 The important results achieved with complexes bearing expanded ring NHC ancillary ligands in catalytic transformations have been attributed to the strong binding of the electron-rich carbene to the metal center that helps the metal retain its ligand, which provides the compound a longer catalyst life time, thus affording enhanced activity 106,126 Cavell et al have reported the synthesis of the first eight-membered ring (diazocanylidene) NHCs 43 through the reaction of the corresponding cyclic amidinium salt 44 with KHMDS.…”