The phosphaguanidinate rare-earth-metal bis(aminobenzyl) complexes [(Ph2P)C(NC6H3iPr2-2,6)2]Ln(CH2C6H4 NMe2-o)2 (Ln = Y(1-Y) and Lu(1-Lu)) were synthesized by the protonolysis of (Ph2P)[C(NHR)(NR)] (R = 2,6-(iPr)2C6H3) with Ln(CH2C6H4NMe2-o)3 (Ln = Y and Lu). Interestingly, the ring-opening rearrangement product [o-Me2NC6H4CH2C(NC6H3iPr2-2,6)2]Lu(CH2C6H4NMe2-o)[O(CH2)4PPh2] (2) was obtained when the acid-base reaction was carried out in THF solution at 60 °C for 36 h. Additionally, the trinuclear homometallic yttrium multimethyl/methylidene complex {[(Ph2P)C(NC6H3iPr2-2,6)2]Y(μ-Me)}3(μ3-Me)(μ3-CH2) (3) was synthesized by the treatment of 1-Y with AlMe3 (2 equiv.) in toluene at ambient temperature in a good yield. However, the binuclear lutetium methyl complex {[(Ph2P)C(NC6H3iPr2-2,6)2]Lu(μ-Me)Me}2 (4) can be generated through the same synthetic method. Likewise, the heterobimetallic Ln-Al complexes [(Ph2P)C(NC6H3iPr2-2,6)2]Ln(Me)(AlMe4) (Ln = Y(6-Y) and Lu(6-Lu)) were afforded from the treatment of complex 1 with AlMe3 (3 equiv.) at ambient temperature for 6 h. Interestingly, upon extending the reaction time of the treatment of 1-Y with three equivalents of AlMe3, the phosphaguanidinate binuclear yttrium carbyne complex [(Ph2P)C(NC6H3iPr2-2,6)2]2Y2(μ4-CH)(μ-Me)(AlMe3)2 (7) and the yttrium carbide complex [(Ph2P)C(NC6H3iPr2-2,6)2]2Y2(μ5-C)(AlMe2)(μ-Me)(AlMe3)2 (8) were isolated via multiple C-H bond activation reactions. Furthermore, the heterobimetallic Y-Al complex [(Ph2P)C(NC6H3iPr2-2,6)2]Y(AlMe4)2 (9) was also obtained from the treatment of 1-Y with four equivalents of AlMe3.