Tertiary Amines and Phosphines

Handbook of Ring-Opening Polymerization. Edited by P. Dubois, O. Coulembier, and J.-M. Raquez Copyright 2009 WILEY-VCH Verlag GmbH Co. KGaA, Weinheim ISBN 978-3-527-31953-4 

The application of DMAP as a catalyst for the ROP of lactide has been exploited in the synthesis of hyperbranched poly(D-mannan)-b-poly(lactic acid) [3] and poly(lactic add)-b-dendritic poly(L-lysine) [4] block copolymers, as well as in the synthesis of fimctional/substituted poly(glycolic acids) [5]. DMAP was shown recently also to catalyze the ROP of eoprolactone in the synthesis of a chitosan-gro/t-poly(E-caprolactone) [6]. 

In a subsequent study, Hedrick and coworkers demonstrated that nucleophilic phosphines were also able to act as highly efficient ROP catalysts [7]. In this example, it was necessary to perform the polymerizations in bulk at high temperature, whereupon the catalyst concentration was found to have a significant effect on the control of the polymerization, with lequiv. (relative to initiator) resulting 

---

Dispersed phase polymerisation of HIPEs has also been used to prepare polymer-supported quaternary onium phase transfer catalysts [162]. One strategy involved the polymerisation of a concentrated emulsion of vinyl benzyl chloride (VBC) in water and subsequent quaternisation of the polymer resin with tertiary amines and phosphines (Fig. 22). 

TERTIARY AMINE AND PHOSPHINE ADDUCTS OF GALLIUM TRIHYDRIDE... 

Tertiary amines and phosphines have received the most attention, but the use of the strong base Me3P=CH3 should be noted, e.g. (entry 19),... 

Rapid polymerization followed when the monomer was added to tertiary amines and phosphines such as triethylamine, triethylphosphine, JV-ethylpiperidine, or pyridine. However, polymerizations initiated by tertiary amines with bulky substituents took hours rather than minutes. Primary and secondary amines were even less effective, whereas aromatic amines such as aniline and N, iV-dimethyl-p-toluidine did not cause polymerization. 

Secondary and tertiary amines and phosphines have been found to he effective but not very strong catalysts. Hy polymerizing at in dimethylform-... 

Alkyl cyanoacrylates are used extensively as instant adhesives and are grouped with vinylidene cyanide, methylene malonates, and a-cyanosorbates at the top of the anionic reactivity scale. As well as readily polymerizing in the presence of conventional anionic initiations such as Bu"Li, they also react readily with tertiary amines and phosphines. Pepper and Johnstonhave examined the catalytic action of triethylphosphine and pyridine at —78 °C in tetrahydrofuran. The former initiator appears to add rapidly and irreversibly to monomer to yield a conventional living anionic polymerization. With pyridine, however,... 

Early studies on pivalolactone (1, ) established that Its polymerization Is Initiated by tertiary amines and phosphines. The reaction was visualized as occurring in two steps. 

Dimethylamine-borane is a white crystalline compound, soluble in many organic solvents, as are other amine-boranes. Unlike most borane adducts of tertiary amines and phosphines, it is also soluble in water. The vapor pressure of the adduct is 0.1 torr at 25°.10 The compound is reasonably stable in neutral or basic aqueous solution at room temperature but decomposes in acidic solution. On heating, dimethylamine-borane loses hydrogen to form dimethylamino-borane.11... 

Organic bases such as tetraalkylammonium hydroxides, tertiary amines, and phosphines [46,49,52-54] were employed as additives to improve the activity and selectivity of platinum catalysts in the oxidation of L-sorbose to 2-keto-L-gulonic acid (2-KLG). Rate acceleration was attributed to a beneficial effect of the amine on the hydration of the intermediate aldehyde. The selectivity enhancement obtained with hexamethylenetetramine (HMTA) was attributed to a steric effect involving a complex between HMTA and L-sorbose via hydrogen bonding [52] (see Section 9.3.3.2). 

Anionic polymerizations are initiated in polar systems by bases and Lewis bases. For example, alkali metals, alcoholates, metal ketyls, metal alkyls, amines, phosphines, and Grignard compounds act as initiators. However, the polymerization mechanism does not depend on the nature of the initiator alone. For example, tertiary amines and phosphines do not only initiate anionic polymerizations under certain conditions, they can also initiate zwitterion polymerizations. In addition, polyinsertions can proceed in less polar systems. Thus, anionic polymerizations are often carried out in polar solvents. Ethers and nitrogen compounds, such as tetrahydrofuran, ethylene glycol dimethyl ether (glyme), diethylene glycol dimethyl ether (diglyme), pyridine, and ammonia are most commonly used. 

The organic compounds of the elements of Group I to III possess vacant valence orbitals and hence are able to function as Lewis acids. They therefore form adducts with electron pair donors such as ethers, tertiary amines and phosphines. This coordination chemistry is discussed further on p. 82. In general the lower the electronegativity of the central atom, the stronger the Lewis acidity. If the Lewis base also has an active (acidic) hydrogen atom, the initially formed adduct may eliminate hydrocarbon e.g. 

Nucleophilic reagents include R Cd, NaCH(C02Me)2, R0 , R2NH, activated aromatics such as 1,3-dimethoxybenzene, allylSiMCj, BH and CN". Lithium alkyls in dichloromethane at low temperatures give good results, but not in diethyl ether. Tertiary amines and phosphines form quaternary salts. 

In 2002, Zhu reported an example of oxidative carbon-carbon coupling catalysed by a gold(iii) complex where air was the sole oxidant (Scheme 16.39). Tertiaiy amines were coupled with nitroalkanes or ketones in the presence of 3 mol% of complex XXm. The reaction was carried out using the corresponding nitroalkane or ketone as solvent and in some cases a small amount of methanol was added. In the case of the coupling with ketones, the addition of 4 A molecular sieves and small amounts of acid were proven to be beneficial for the reaction. Remarkably, this protocol could be scaled up and one of the products was successfully prepared on a 1 g scale. The protocol was expanded to the coupling of tertiary amines and phosphine oxides in a later report by the same group. ... 

The polymerisation does not normally have a termination step. This is in contrast to most other anionic polymerisations, which are very sensitive to trace impurities such as components of the atmosphere or moisture (only strong acids are terminating agents) [46]. Other initiators such as tertiary amines and phosphines have been postulated to polymerise via polymeric zwitterions. This mechanism has been proved by the isolation of stable zwitterions [47]. 

In designing an organic catalyst for the ROP of cyclic esters, we turned towards the likely active nucleophilic species of biocatalysis. Lewis bases including tertiary amines and phosphines, pyridines and imidazoles have been shown to be effective nucleophilic catalysts accelerating a wide variety of processes. For example, 4-(dimethylamino)pyridine (DMAP) and related... 

Although the MBH reaction typically relies on tertiary amines and phosphines as the catalysts, Basavaiah and Briere expanded the chlacogenide MBH reaction by using thiolane in the presence of TBDMSOTf. This variant of the MBH was run using 2-cyclohex-1-one 49 and acetals 59 with... 

---