A well-characterised 14-electron rhodium phosphine complex, [Rh(PiPr3)3][BArF4], which contains a beta-CH agostic interaction, is observed to undergo spontaneous dehydrogenation to afford [Rh(PiPr3)2(PiPr2(C3H5))][BArF4]; calculations on a model system show that while C-H activation is equally accessible from the beta-CH agostic species or an alternative gamma-CH agostic isomer, subsequent beta-H-transfer can only be achieved along pathways originating from the beta-CH agostic form.