The effect of substitution on the potential energy surfaces of triple-bonded RIn^PR (R ¼ F, OH, H, CH 3 , SiH 3 , NHC, SiMe(SitBu 3 ) 2 and SiiPrDis 2 ) species was investigated, using the density functional theory (i.e., M06-2X/Def2-TZVP, B3PW91/Def2-TZVP and B97-D3/LANL2DZ+dp). The theoretical results suggest all of the triple-bonded RIn^PR molecules prefer to adopt a bent form with an angle (:In-P-R) of about
90. Present theoretical evidence suggests only the bulkier substituents, in particular for the strong donating groups (such as the NHC group), can greatly stabilize the In^P triple bond. In addition, bonding analyses demonstrate the bonding character of such triple-bonded RIn^PR compounds should be represented as . That is to say, the In^P triple bond contains one traditional s bond, one traditional p bond, and one donor-acceptor p bond. As a consequence, the theoretical findings strongly suggest the In^P triple bond in acetylene analogues (RIn^PR) should be very weak.