Chapter 23
Synthesis and Reactivity of (Silylamino)- and (Silylanilino)phosphines
Downloaded by UNIV OF NORTH CAROLINA on June 21, 2013 | http://pubs.acs.org Publication Date: December 1, 2005 | doi: 10.1021/bk-2005-0917.ch023
Robert H . Neilson, Pradeep Devulapalli, Bethany K. Jackson, Andrew R. Neilson, Sahrah Parveen, and Bin Wang Department of Chemistry, Texas Christian University, Fort Worth, TX 76129
Phosphorus compounds that contain silicon-nitrogen functional groups have a very rich derivative chemistry. The wide variety of reactions that can occur at phosphorus in combination with facile cleavage of the Si-N bond makes them useful precursors to many types of cyclic and polymeric P-N systems. We report here on (a) the synthesis and reactivity of (silylamino)phosphines, including some new systems that contain 4-aryl functional groups on phosphorus, and (b) the synthesis and characterization of two new types of (silylanilino)phosphines that contain either a 4-aryl functional group on nitrogen or a phenylene ring between nitrogen and phosphorus. These anilino derivatives are potential precursors to poly(phenylenephosphazenes), a new class of inorganic— organic hybrid polymers in which phosphazene (R P=N) and phenylene (C H ) units alternate along the backbone. 2
6
4
© 2006 American Chemical Society
In Modern Aspects of Main Group Chemistry; Lattman, M., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2005.
325
326 The preparative chemistry of compounds containing the Si-N-P linkage has been extensively developed over the last three decades (/). These studies have led to a number of synthetically useful reagents and methods in phosphorusnitrogen chemistry. Depending on the types of substituents present on the three main group elements, and on the oxidation state and coordination number at phosphorus, such compounds are useful precursors to cyclic and polymeric poly(phosphazenes), [R P=N] , as well as various low-coordinate phosphorus systems containing P=N or P=C (ρ-ρ)π bonds. In this paper, we will (a) review the chronological development of an important series of Si-N-P compounds, the (silylamino)phosphines, and (b) briefly summarize our recent results in this area including the synthesis of some new 4-aryl fiinctionalized derivatives as well as some related (silylanilino)phosphines.
Downloaded by UNIV OF NORTH CAROLINA on June 21, 2013 | http://pubs.acs.org Publication Date: December 1, 2005 | doi: 10.1021/bk-2005-0917.ch023
2
n
(Silylamino)phosphines As reported by Cowley et al (2), some of the first (silylamino)phosphines, were prepared by treating phosphorus(III) halides with lithium bis(trimethylsilyl)amide (eq 1). At that time, these novel products were mainly of interest in relation to certain bonding and structure questions, including the determination of P-N bond rotation barriers by dynamic NMR measurements. ρχ (Me Si) NU 3
2
3
— -
N-P
m
R = F,Cl,CF ,Me 3
For the preparation of organo-substituted derivatives (e.g., R = alkyl), however, this method is severely limited by the practical difficulties in preparing, storing, and handling large quantities of hazardous reagents like Me2PCl. Thus, we were led to search for alternative synthetic routes to these systems. The most useful synthetic entry to Si-N-P systems is the Wilburn method (3) (eqs 2 - 4) in which phosphorus halides are successively treated with silylamides and organometallic reagents. This is generally a convenient, one-pot synthesis of a wide variety of both symmetrical (1) and unsymmetrical (2 and 3) diorgano substituted (silylamino)phosphines. In cases with R groups more sterically demanding than methyl or ethyl, it is possible to isolate the mono-substituted chlorophosphines (4) (4).
In Modern Aspects of Main Group Chemistry; Lattman, M., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2005.
327 (1) PC1
(Me Si) N-P
3
3
(Me Si) NH 3
2
(2)
N
(2) 2 RMgBr
2
M-BuLi (l)PhPCl
(Me Si) NLi 3
2
2
Ph (Me-jSi^N-P^
(3)
(Me Si) N-P
(4)
(2) RMgBr (1)PC1 Downloaded by UNIV OF NORTH CAROLINA on June 21, 2013 | http://pubs.acs.org Publication Date: December 1, 2005 | doi: 10.1021/bk-2005-0917.ch023
3
\(2) RMgBr 1
Z (Me Si) N-P 3
2
RMgBr
3
x
2
x
R'
CI
The (silylamino)phosphines (1 - 3) are then routinely converted to NsUylphosphoranimines (5) (eq 5) by sequential oxidative halogenation and substitution reactions (J). Subsequent thermolysis of these Nsilylphosphoranimines (5) readily affords poly(alkyl/arylphosphazenes) (6) (eq 6) via a condensation polymerization process (
