Acyclic catena-diphosphinodiphosphonium dications [R3P- PR′-PR′-PR3]2+ or bisphosphine-diphosphenium complexes [R3P→PR′-PR′←PR3] 2+: Synthesis by reductive P-P coupling of [R3P-

Article abstract of DOI:10.1021/ja062972y

The acyclic tetraphosphorus dication [Ph₃P-PPh-PPh-PPh₃]²⁺ has been formed by the reductive coupling of [Ph₃P-PPhCl]⁺, providing a new synthetic method for the systematic development of catena-phospho

Full text of DOI:10.1021/ja062972y

Published on Web 07/08/2006
Acyclic catena-Diphosphinodiphosphonium Dications [R3P-PR′-PR′-PR3]2+ or
Bisphosphine-Diphosphenium Complexes [R3PfPR′-PR′rPR3]2+: Synthesis
by Reductive P-P Coupling of [R3P-PR′Cl]+ and Phosphine Ligand Exchange
C. Adam Dyker,† Neil Burford,*,† Michael D. Lumsden,‡ and Andreas Decken§
Department of Chemistry, Dalhousie UniVersity, Halifax, NoVa Scotia B3H 4J3, Canada, Atlantic Region Magnetic
Resonance Center, Dalhousie UniVersity, Halifax, NoVa Scotia B3H 4J3, Canada, and Department of Chemistry,
UniVersity of New Brunswick, Fredericton, New Brunswick E3A 6E2, Canada
Received April 28, 2006; E-mail: Neil.Burford@dal.ca
Catenation is the property of carbon that is principally responsible
for the extent of organic chemistry. The established series of catena-
phosphines1-4 and catena-phosphorus anions1-3;5 highlight an
analogous prominence for homoatomic bonding in phosphorus
chemistry. We have been systematically developing catena-
phosphorus cations, composed of the familiar phosphine and
phosphonium units,6-9 as compounds that define a potentially
extensive and diverse new direction in fundamental phosphorus
chemistry. Here we report the synthesis, characterization, and ligand
exchange reactivity of the first acyclic tetraphosphorus dications.
31P NMR spectra of reaction mixtures containing PhPCl2, Ph3P,
and TMSOTf (1:1:1 molar ratio) in CH2Cl2 show rapid and
quantitative formation of the chlorophosphinophosphonium salt
1a[OTf] (eq 1). Sharp singlets (22 and 55 ppm) observed at room
Figure 1. Solid-state structure of one enantiomer of the cation in racemic
1a[OTf]: P1-P2 ) 2.2471(8) Å, P2-Cl ) 2.0595(9) Å.
temperature resolve into the expected doublets (1JPP ) 333 Hz) at
-60 °C. The solid-state structure of the cation is shown in Figure
1.
After 2 days, reactions containing excess Ph3P and TMSOTf give
[Ph3PCl][OTf] (31P: ) 66 ppm),10,11 and a new salt has been
isolated and characterized as 2a[OTf]2. We conclude that Ph3P
effects the reductive coupling of two 1a cations according to eq 2.
The overall process is summarized in eq 3 and is distinct from the
previously reported reaction of PhPCl2, Ph3P, and AlCl3 that gives
Figure 2. Solid-state structure of the dication in meso-2a[OTf]2: P1-P2
) 2.2583(10) Å, P2-P2′ ) 2.2214(13) Å.
[Ph3P-PPh-PPh3][AlCl4]2.12
Single crystals of 2a[OTf]2 reveal the meso-(S,R) configuration
of the dication in the solid state (Figure 2), which is consistent
with the analogous neutral 2,3-diphosphino-1,4-diphosphorane.13
Solid samples of 2a[OTf]2 exhibit reproducible FT-IR data;
however, NMR spectra (Figure 3) of the reaction mixture (31P) and
of dissolved crystalline material (31P and 1H) consistently show the
presence of two diastereomers (de ) 62%, by 1H NMR) in solution,
indicating that solutions of 2a[OTf]2 contain all three stereoisomers.
All three isomers of the “naked” anion [PhP-PPh-PPh-PPh]2- exist
in the solid state.5 The 31P NMR spectrum for the major isomer of
2a has been simulated as an AA′BB′ spin system and is tentatively
assigned to the meso-(S,R) isomer based on the steric preference
† Department of Chemistry, Dalhousie University.
‡ Atlantic Region Magnetic Resonance Center, Dalhousie University.
§ Department of Chemistry, University of New Brunswick.
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10.1021/ja062972y CCC: $33.50 © 2006 American Chemical Society

C O M M U N I C A T I O N S
meso-2b[OTf]2 (Figure 4) have been characterized. Reactions of
2a[OTf]2 with one equivalent of PMe3 give a 1:1 mixture of 2a
and 2b.
Cations 2a and 2b represent the first derivatives of acyclic
catena-tetraphosphorus dications and are new members of a scarcely
explored family of catena-phosphorus dications with topologies 3,14
4,15 5,16 6,12 and 7.17-22 The reductive coupling of 1a represents a
rational and potentially versatile, synthetic method to diversify and
extend catena-phosphorus chemistry. In addition, the recognition
of 2 as a bisphosphine complex of a catena-diphosphenium dication
(2′) is expected to provide a synthon to a vast array of new
polyphosphorus coordination complexes by the introduction of an
appropriate Lewis base.
Figure 3. 31P{1H} NMR spectrum (101.3 MHz) for 2a[OTf]2 with the
simulated (inverted) AA′BB′ spectrum for the meso-(S,R) isomer (δ )
-33, 24 ppm); * refers to peaks for the minor isomers (R,R and S,S) (δ )
-42, 22 ppm).
Acknowledgment. We thank the Natural Sciences and Engi-
neering Research Council of Canada, the Killam Foundation, the
Canada Research Chairs Program, the Canada Foundation for
Innovation, the Nova Scotia Research and Innovation Trust Fund,
and the Walter C. Sumner Foundation for funding.
Supporting Information Available: Experimental details, char-
acterization data, and CIF files. This material is available free of charge
via the Internet at http://pubs.acs.org.
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