Diamond electrodes doped with this element may be used in organic electro-synthesis due to their large electrochemical window. Hydroxylation reactions often use a disiamyl-substituted compound of this element. A bulky compound of this element and a phosphine form the classic frustrated Lewis pair. A base attacks this element before transmetallating an aryl group onto palladium in the (*) Suzuki coupling. This element adds across a double bond, followed by oxidation with a peroxide, in an anti-Markovnikov (-5[1])addition of water across (10[1])a double bond. This element’s trihydride (10[1])dimerizes into a compound with two three-center, two-electron bonds, since this element typically only forms three covalent bonds in violation of the octet rule. (10[1])For 10 points, name this trivalent element whose atomic number is 5. ■END■