Abstract
The trifunctional P/B/B frustrated Lewis pairs 11a-c featuring bulky aryl groups at phosphorus [Dmesp (a), Tipp (b), Mes* (c)] react with H2 by heterolytic hydrogen splitting followed by cleavage of HB(C6F5)2 to give the zwitterionic six-membered heterocyclic PH phosphonium/borate products 14a-c. Compounds 11a,b react with carbon monoxide by means of a Lewis acid induced CO insertion/rearrangement sequence that eventually results in the formation of the macrocyclic dimers 17a,b. The respective carbonylation reaction of the Mes*P/B/B FLP gives the macrocyclic trimer 18c. The new products were characterized spectroscopically and by X-ray diffraction and the reaction mechanism was analyzed by DFT calculations.
Highlights
Macrocyclic compounds have very interesting structural features.[1,2] Many such systems play signi cant roles in medicine and biology[3,4,5,6,7] and many serve as important chemical reagents.[8,9,10,11,12] Macrocyclic ring closure is o en difficult to achieve selectively since ring closure principally competes with entropically favoured formation of the linear oligomers
The trifunctional P/B/B frustrated Lewis pairs 11a–c featuring bulky aryl groups at phosphorus [Dmesp (a), Tipp (b), Mes* (c)] react with H2 by heterolytic hydrogen splitting followed by cleavage of HB(C6F5)[2] to give the zwitterionic six-membered heterocyclic PH phosphonium/borate products 14a–c
Compounds 11a,b react with carbon monoxide by means of a Lewis acid induced CO insertion/rearrangement sequence that eventually results in the formation of the macrocyclic dimers 17a,b
Summary
Macrocyclic compounds have very interesting structural features.[1,2] Many such systems play signi cant roles in medicine and biology[3,4,5,6,7] and many serve as important chemical reagents.[8,9,10,11,12] Macrocyclic ring closure is o en difficult to achieve selectively since ring closure principally competes with entropically favoured formation of the linear oligomers. Endergonic opening of the P/B linkage of 11b yields the reactive P/B/B intermediate 11open, which may undergo the typical 1,1-P/B FLP addition reaction to carbon monoxide.[35,36] Carbonyl activation by the remaining pendent –B(C6F5)[2] functionality[70,71] via 16A might initiate the kinetically facile and thermodynamically feasible formation of the CO insertion product32 16B.
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