The reaction between Mo(O)(CHAro)(ORF6)(2)(PMe3) (Ar-o = ortho-methoxyphenyl, ORF6 = OCMe(CF3)(2)) and 2 equiv of LiOHMT (OHMT = O-2,6-(2,4,6-Me3C6H2)(2)C6H3) leads to Mo(O)(CHAro)(OHMT)(2), an X-ray structure of which shows it to be a trigonal bipyramidal anti benzylidene complex in which the o-methoxy oxygen is coordinated to the metal trans to the apical oxo ligand. Addition of 1 equiv of water (in THF) to the benzylidyne complex, Mo(CArp)(OR)(3)(THF)(2) (Ar-p = para-methoxyphenyl, OR = ORF6 or OC(CF3)(3) (ORF9)) leads to formation of {Mo(CArp)(OR)(2)(mu-OH)(THF)}(2)(mu-THF) complexes. Addition of 1 equiv of a phosphine (L) to Mo(CArp)(ORF9)(3)(THF)(2) in THF, followed by addition of 1 equiv of water, all at room temperature, yields Mo(CArp)(ORF9)(2)(L) complexes in good yields for several phosphines (e.g., PMe2Ph (69% by NMR), PMePh2 (59%), PEt3 (69%), or P(i-Pr)(3) (65%)). The reaction between Mo(O)(CHArp)(ORF9)(2)(PEt3) and 2 equiv of LiOHMT proceeds smoothly at 90 degrees C in toluene to give Mo(O)(CHArp)(OHMT)(2), a four-coordinate syn alkylidene complex. Mo(O)(CHArp)(OHMT)(2) reacts with ethylene (1 atm in C6D6) to give (in solution) a mixture of Mo(O)(CHArp)(OHMT)(2), Mo(O)(CH2)(OHMT)(2), and an unsubstituted square pyramidal metallacyclobutane complex, Mo(O)(CH2CH2CH2)(OHMT)(2), along with ethylene and ArpCH=CH2. Mo(O)(CHArp)(OHMT)(2) also reacts with 2,3-dicarbomethoxynorbornadiene to yield syn and anti isomers of the "first-insertion" products that contain a cis C=C bond.