German Edition: DOI: 10.1002/ange.201710099 Cyclic Phosphines International Edition: DOI: 10.1002/anie.201710099 L 3 C 3 P 3 : Tricarbontriphosphide Tricyclic Radicals and Cations Stabilized by Cyclic (alkyl)(amino)carbenes Zhongshu Li, Yuanfeng Hou, Yaqi Li, Alexander Hinz, JeffreyR. Harmer,* Cheng-Yong Su,* Guy Bertrand, and Hansjçrg Grützmacher* Dedicated to Professor Dieter Fenske on the occasion of his 75th birthday Abstract: Alkynes usually oligomerize to give rings with a conjugated p-electron system. In contrast, phosphaalkynes, R  C  P, frequently give compounds with polycyclic structures, which are thermodynamically more stable than the corre- sponding p-conjugated isomers. The syntheses of the first C 3 P 3 tricyclic compounds are reported with either radical or cationic ground states stabilized by cyclic (alkyl)(amino)carbenes (CAACs). These compounds may be considered as examples of tricarbontriphosphide coordinated by carbenes and are likely formed via trimerization of the corresponding mono- radicals CAAC-CPC . The mechanism for the formation of these tricarbontriphosphide radicals has been rationalized by a com- bination of experiments and DFT calculations. Organophosphorus compounds with C n P n polycyclic skel- etons that are exclusively composed of carbon and phospho- rus atoms are still relatively rare and their properties remain to be explored. To the best of our knowledge, all of the reported C n P n polycyclic compounds are prepared by oligo- merization of phosphaalkynes, mainly tBu C P. [1] For instance, phosphaalkyne tetramers A and B (Scheme 1) could be prepared via thermally induced or metal-mediated oligomerization. [2, 3] Other polycyclic types of tetramers, pentamers, and even hexamers are also obtained from the corresponding phosphaalkynes. [1] Remarkably, stable poly- cyclic skeletons of the composition C 3 P 3 seemingly have never been isolated, while 1,3,5-triphosphabenzenes C and 1,3,5- triphospha-Dewar-benzenes D are well established and their conversion into polycyclic compounds with additional reagents is documented. [1, 3b] This agrees well with calculations on (H,C,P) 3 isomers, which predict that the cyclic triphos- phabenzenes are more than 30 kcal mol 1 lower in energy than prismane cages. [4] Singlet N-heterocyclic carbenes (NHCs) [5] and cyclic diamidocarbenes (DACs) [6] may stabilize otherwise reactive molecules, and recently cyclic and acyclic C 2 P 2 skeletons as possible forms of “dicarbondiphosphide” could be isolated with these as substituents. [7] Herein we report the synthesis of neutral tricarbontriphosphide radicals (L 3 C 3 P 3 )C and their oxidation to the corresponding cations (L 3 C 3 P 3 ) + (L = CAAC). Phosphaketenes such as 1 are easily prepared from chlorodiazaphospholenes and Na(OCP) [7] and are quantita- tively rearranged to phosphaallenes L = C = P[PO(NDipp) 2 - (CH) 2 ] upon reaction with diisopropylphenyl (Dipp)-substi- tuted NHC or DAC as carbene L. [7a, 8] These phosphaallenes cleanly react with KC 8 to give the anionic oxydiazaphospho- lene 3 and cyclic or acyclic dicarbondiphosphide compounds L 2 C 2 P 2 (L = NHC, DAC). [8] Carbene-bound CP radicals L =C =PC 4 may be formed as first intermediates. We reasoned that with sterically less demanding carbenes higher oligomers of these radicals may be obtained. Cyclic (alkyl)- (amino)carbenes, CAACs, can be easily prepared on a multi-gram scale and their steric demand can be facilely tuned. [9] Phosphaketene 1 [8] was reacted with CAACs L 1 –L 5 (Scheme 2). All reactions yield phosphaallenes 2 as bright Scheme 1. Possible structures for tetra- or trimers of RC P. * = CR with R = H, organyl groups. [*] Dr. Z. Li, Y. Hou, Y. Li, Prof.Dr. C.-Y. Su, Prof.Dr. H. Grützmacher Lehn Institute of Functional Materials (LIFM), School of Chemistry, Sun Yat-Sen University 510275 Guangzhou (China) E-mail: cesscy@mail.sysu.edu.cn Dr. A. Hinz University of Oxford, Chemistry Research Laboratory 12 Mansfield Road, OX1 3TA, Oxford (UK) Prof. Dr. J. R. Harmer Centre for Advanced Imaging, University of Queensland Brisbane, QLD, 4072 (Australia) E-mail: jeffrey.harmer@cai.uq.edu.au Prof. Dr. G. Bertrand UCSD/CNRS Joint Research Chemistry Laboratory, Department of Chemistry, University of California San Diego La Jolla, CA 92521-0403 (USA) Prof. Dr. H. Grützmacher Department of Chemistry and Applied Biosciences, ETH Zurich 8093 Zurich (Switzerland) E-mail: hgruetzmacher@ethz.ch Supporting information and the ORCID identification number(s) for the author(s) of this article can be found under: https://doi.org/10.1002/anie.201710099. A ngewandte Chemie Communications 198  2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim Angew. Chem. Int. Ed. 2018, 57, 198 –202