Deuterium-labeled compounds are essential in chemistry and life sciences, particularly in drug discovery. As a stable hydrogen isotope, deuterium aids in mechanistic studies, mass spectrometry, and deuterated drug development. Benzylic positions are prone to oxidative metabolism, but the greater stability of C-D bonds can influence drug absorption, distribution, metabolism, and excretion. Thus, significant efforts focus on late-stage benzylic deuteration. Transition-metalcatalyzed C-H activation and hydrogen transfer reactions are widely used, but selective benzylic deuteration remains challenging due to competing C-H labeling, especially without directing heteroatoms. Encouraged by our results on C-P bond hydrolysis, we anticipated that benzhydryl triarylphosphonium salts 11 could offer a valuable opportunity for benzylic deuterium labeling-not just once, but twice, allowing the incorporation of two deuterium atoms. We hypothesize that this can be achieved through the synergistic deuterolysis of the benzylic C-H and C-P bonds. Replacing water with D₂O enabled the synthesis of fully α-deuterated unsymmetrical diarylmethanes (13) with excellent deuterium incorporation (up to 99%) and good yields (Figure ). Notably, we successfully synthesized D-labeled unsymmetrical diarylmethanes 13 bearing ortho-, meta-, and parasubstituted halides, including -F (13k-n), -Cl (13h-i), and -Br (13j and 13u). The reaction was also effective in affording D-labeled unsymmetrical diarylmethanes with various functional groups, such as -OMe (13b-e), -NO₂ (13s), indole (13u-w), 1,3-benzodioxole (13x), and furan (13t). A proposed mechanism for the deuterolysis-(and hydrolysis-) based reduction pathway is shown in Figure . Based on literature reports, this process involves the formation of ylide/ylene 16, followed by protonation or deuteration of ylene 16. The subsequent cleavage of the C(sp³)-P⁺ bond occurs via P-selective nucleophilic substitution (See 16 to 13), releasing triphenylphosphine oxide (Ph₃P=O). To further support this mechanism through the generation of the ylene 16 intermediate, a hydrolysisreduction reaction of the benzylic deuterated benzhydryl triarylphosphonium salt 11a d with H₂O was performed, affording the hydrolysis product with complete loss of deuterium incorporation falls to 0%. 1