The structural and reactive properties of the acetyl-protected "one-legged" manganese porphyrin [SAc]P-Mn(III)Cl on Ag(100) have been studied by NEXAFS, synchrotron XPS and STM. Spontaneous surface-mediated deprotection occurs at 300 K accompanied by spreading of the resulting thio-tethered porphyrin across the metal surface. Loss of the axial chlorine ligand occurs at 498 K, without any demetalation of the macrocycle, leaving the Mn center in a low co-ordination state. At low coverages the macrocycle is markedly tilted toward the silver surface, as is the phenyl group that forms part of the tethering "leg". In the monolayer region a striking transition occurs whereby the molecule rolls over, preserving the tilt angle of the phenyl group, strongly increasing that of the macrocycle, decreasing the apparent height of the molecule and decreasing its footprint, thus enabling closer packing. These findings are in marked contrast with those previously reported for the corresponding more rigidly bound four-legged porphyrin [ Turner , M. , Vaughan , O. P. H. , Kyriakou , G. , Watson , D. J. , Scherer , L. J. , Davidson , G. J. E. , Sanders , J. K. M. and Lambert , R. M. J. Am. Chem. Soc. 2009 , 131 , 1910 ] suggesting that the physicochemical properties and potential applications of these versatile systems should be strongly dependent on the mode of tethering to the surface.