Single crystals of boron-doped Ba_8Al_(14)Si_(31) clathrate I phase were prepared using Al flux growth. The structure and elemental composition of the samples were characterized by single-crystal and powder X-ray diffraction; elemental analysis; and multinuclear ^(27)Al, ^(11)B, and ^(29)Si solid-state NMR. The samples' compositions of Ba_8B_(0.17)Al_(14)Si_(31), Ba_8B_(0.19)Al_(15)Si_(31), and Ba_8B_(0.32)Al_(14)Si_(310) were consistent with the framework-deficient clathrate I structure Ba_8Al_xSi_(42-3/4x)□_(4-1/4x) (X = 14, □ = lattice defect). Solid-state NMR provides further evidence for boron doped into the framework structure. Temperature-dependent resistivity indicates metallic behavior, and the negative Seebeck coefficient indicates that transport processes are dominated by electrons. Thermal conductivity is low, but not significantly lower than that observed in the undoped Ba_8Al_(14)Si_(31) prepared in the same manner
