The reaction of amido-substituted stannylenes with phospha-Wittig reagents (Me3PPR) results in release of hexamethyldisilazane and tethering of the resulting −CH2PMe2PR fragment to the tin center to give P-donor stabilized stannylenes featuring four-membered Sn,C,P,P heterocycles. Through systematic increases in steric loading, the structures of these systems in the solid state can be tuned, leading to successive P–P bond lengthening and Sn–P contraction and, in the most encumbered case, to complete P-to-Sn transfer of the phosphinidene fragment. The resulting stannaphosphene features a polar SnP double bond as determined by structural and computational studies. The reversibility of phosphinidene transfer can be established by solution phase measurements and reactivity studies.