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Synthesis of novel aminomethylphosphine complexes

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posted on 2015-06-23, 10:48 authored by Nuria Lastra Calvo
A new series of aminomethylphosphine ligands incorporating a PCN backbone and a pendant amine were synthesised using a phosphorus Mannich condensation reaction. Their coordination capabilities were investigated with late transition metal centres. Following a procedure well established within our research group, several phosphines were obtained using {P(CH2OH)4}Cl (THPC) in two steps. Firstly, THPC was reacted with various ortho and para anilines to give phosphonium salts P{CH2N(H)R}4Cl (R = C6H5, o–MeC6H4, o– i PrC6H4, o–t BuC6H4, o–FC6H4, o–CF3C6H4, o–{C(Me)=CH2}C6H4, p–MeC6H4, p–i PrC6H4, p–FC6H4 and p–EtC6H4). Secondly, these new salts were reacted with Et3N to obtain the cyclic RN(H)CH2P{(CH2)3(NR)2} phosphines (R = para–substituted anilines) or with KOt Bu to obtain acyclic P{CH2N(H)R}3 phosphines (R = ortho-substituted anilines) and cyclic P{CH2N(R)CH2}2P diphosphines (R = ortho–substituted anilines). Double condensation was observed in the 31P{1 H} NMR of cyclic phosphines RN(H)CH2P{(CH2)3(NR)2} to form {(CH2)3(NR)2}PCH2N(R)CH2P{(CH2)3(NR)2} diphosphines. Some cyclic phosphines were investigated under a wide range of conditions with Ph2PCH2OH giving asymmetric Ph2PCH2N(R)CH2P{(CH2)3(NR)2} diphosphines along with symmetric diphosphines counterparts and other phosphorus coproducts according to 31P{1 H} NMR and MS. A novel bicyclic OP{CH2N(R)CH2}3PO diphosphine (R = p–MeC6H4) was obtained as crystalline solid from the filtrate of the reaction between RN(H)CH2P{(CH2)3(NR)2} and Ph2PCH2OH and it was characterised by X–ray spectroscopy. Attempts to synthesise this diphosphine from P(CH2OH)3 and p–MeC6H4 were unsuccessful. The family of aminomethylphosphine ligands was extended by treating Ph2PCH2OH or CgPCH2OH (Cg = 1,3,5,7–tetramethyl–2,4,8–trioxa–6–phosphaadamantane) with various primary amines to afford R(H)NCH2PR’2 (R’ = Cg or Ph). Symmetric Ph2PCH2N(R)CH2Ph2 diphosphines were observed in the 31P{1 H} NMR spectra indicating that phosphines with Ph2P– moiety were more susceptible to undertake a second condensation. Novel asymmetric o–{Ph2PCH2C(H)(CH3)}C6H4N(H)CH2PPh2 diphosphine was synthesised by treatment of o-{C(Me)=CH2}C6H4NH2 with Ph2PH to afford o– {Ph2PCH2C(H)(CH3)}C6H4NH2 followed by condensation of the amino group with Ph2PCH2OH. Analogous o–{CgPCH2C(H)(CH3)}C6H4NH2 phosphine was also obtained. The coordination capabilities of selected compounds was studied with late transition metal precursor such as Pt(II), Pd(II) and Ru(II). Monophosphine compounds acted as Pmonodentate ligands to form square planar cis and trans MCl2L2 (M = Pt and Pd) complexes. However, whereas cyclic ligands RN(H)CH2P{(CH2)3(NR)2} afforded cisMCl2L2, acyclic ligands P{CH2N(H)R}3 afforded trans-MCl2L2 along with cis-PtCl2L2 in some cases. Those phosphines which conducted double condensation adopted a P,Pchelate mode to form a 6–membered M–P–C–N–C–P to afford cis-MCl2L (M = Pt and Pd). More interesting is the rarely observed P,P-bridging mode exhibited by P{CH2N(R)CH2}2P ligands to form homobimetallic cis–(PtCl2L)2 complexes and {RhCl2(η5 –Cp*)}2L complexes. These metal compounds were obtained and characterised by in situ NMR however their structures were further supported by simulated 31P{1 H} NMR and X–ray studies. Asymmetric Ph2PCH2N(R)CH2P{(CH2)3(NR)2} diphosphines coordinated to Pt(II) in a P,P–chelate fashion affording a mixture of cis and trans bis(chelate) (PtL2)Cl2. Complex in trans geometry was isolated and the structure was further supported by X–ray crystallography. The coordination capabilities of the ligands were investigated with Ru(II) metal centre revealing “piano–stool” structure of the type RuCl2(η6 –p–cymene)L where the monophosphines adopted a P-monodentate mode and {RuCl2(η6 –p–cymene)}2L where the diphosphines adopted a P,P-bridging mode. Preliminary studies with selected Ru complexes were carried out to investigate their potential catalytic activity to trap CO2 by its insertion into the Ru–Cl bond which suggested that the chloride needs to be substituted by a hydride prior the CO2 insertion. Compounds were characterised by spectroscopic techniques and the structure of some phosphines was further supported by X–ray crystallography.





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© N. Lastra Calvo

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This work is made available according to the conditions of the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0) licence. Full details of this licence are available at: https://creativecommons.org/licenses/by-nc-nd/4.0/

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A Doctoral Thesis. Submitted in partial fulfilment of the requirements for the award of Doctor of Philosophy of Loughborough University.


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