DOI: 10.1002/chem.200600120 Quantification of Ultrasound-Induced Chain Scission in Pd II –Phosphine Coordination Polymers Jos M. J. Paulusse, Jeroen P. J. Huijbers, and RintP. Sijbesma* [a] Introduction Reversible coordination polymers are dynamic supramolec- ular polymers [1,2] with coordinative bonds in their main chain. Much attention in this relatively new research area is directed towards the characterization of the dynamic proper- ties of these polymers, such as exchange kinetics, [3] ring– chain equilibria, [4–6] solvent interactions, [6,7] and new metal– ligand combinations. [8] At the same time, coordination poly- mers are already beginning to find applications as smart ma- terials, for instance, as stimuli-responsive [9] and photoactive polymers. [10,11] Our interest in this field concerns the direct manipulation of the coordination sphere of transition-metal complexes by mechanical forces. Ultrasound is known as one of the most efficient techniques to break polymers in solution, [12,13] but high molecular weights are required to transduce the mechanical forces. [14] Employing weaker bonds in the polymer chain allows for preferential scission at these bonds over other, stronger bonds. [15,16] Ultrasonica- tion of reversible coordination polymers enables the specific rupture of a coordinative bond. [17] Our ultimate goal is to develop mechanochemical synthetic procedures in coordina- tion chemistry and to enable the mechanical formation of highly active catalytic species. Recently, we reported on the use of ultrasound to reversi- bly break coordination polymer 1, which is based on diphe- nylphosphine telechelic poly(tetrahydrofuran) and palladi- um(ii ) dichloride. [17] The weight-averaged molecular weight (M w ) of the coordination polymer was reversibly reduced from 1.710 5 to 1.010 5 gmol 1 upon irradiation with ultra- sound for one hour. Upon equilibration, the original molec- ular-weight distribution was fully restored within 24 h. The reversibility of the ultrasonic scission process indicated that only coordinative bonds and no covalent bonds were Abstract: A kinetically inert, reversible coordination polymer (3) was obtained through complexation of dicyclohexyl- phosphine telechelic poly(tetrahydro- furan) with palladium(ii ) dichloride. This coordination polymer is unreac- tive towards palladium(ii ) dichloride bis(1-diphenylphosphino)dodecane (4), because ligand dissociation in the coor- dination polymer is slow. However, upon ultrasonication of solutions of 3 in toluene in the presence of 4, forma- tion of palladium(ii ) heterocomplexes was observed with 31 P NMR spectro- scopy. Heterocomplex formation, the consumption of 4, and changes in mo- lecular weight were used to quantify the scission process. In the presence of 60 equivalents of the alkyldiphenyl- phosphine stopper complex, the reduc- tion in molecular weight was strongly enhanced; over a period of eight hours the weight-averaged molecular weight was reduced from 1.110 5 to 2.3 10 4 gmol 1 while 47% of the palladi- ACHTUNGTRENNUNGum(ii ) complexes in the coordination polymer had been converted into het- erocomplexes. These results show that the system of 3 in combination with scavenger 4 is a suitable system to study the efficiency of ultrasound-in- duced chain scission of coordination polymers. Keywords: coordination polymers · heterocomplexes · phosphanes · supramolecular chemistry · ultrasound [a] J. M. J. Paulusse, + J. P. J. Huijbers, + Dr. R. P. Sijbesma Laboratory of Macromolecular and Organic Chemistry Eindhoven University of Technology P.O. Box 513, 5600 MB Eindhoven (The Netherlands) Fax: (+ 40)245-1036 E-mail: R.P.Sijbesma@tue.nl [ + ] These authors contributed equally to this work. Supporting information for this article is available on the WWW under http://www.chemeurj.org/ or from the author. # 2006 Wiley-VCH Verlag GmbH&Co. KGaA, Weinheim Chem. Eur. J. 2006, 12, 4928–4934 4928